A contest can be a way of promoting an open call art test of sorts. However make sure you make the rules to your context exceptionally clear for what you are looking for, and what the rewards are.
Rules-
What exactly you want for the contest. Be specific about what you are looking for technically, quality, and style wise. If you provide examples of some kind of what you are looking for. Try to offer some rules for the uniformity you require in order to judge- judging on creativity alone has it's time and place but in a situation like this I would want to feel comfortable with knowing what my judges were looking for.
If you do this via the internet as widely as possible, be aware you may need to set a minimum age for those who enter for legal reasons.
If you ask for a concept to be made of a character (or environment, item, etc.), provide an average amount of information you would provide to this artist in the job so they know what to expect.
If you are looking for something more "advanced" in the pipeline like 3D art, make sure you provide enough so you can reasonably expect to get what you are looking for from most entries.
Position-
What type of artist you are looking for and the expectations you have for the type of art. Depending on the type of art some art categories are more combined and would expect overlap, others may view them as more seperate (environment/character/concept splits for example, or a generalist/multi-discipline).
Rewards-
If this is a job and will result in pay and benefits make sure that is clear, because most artists will decline work where the "payment" is ambiguous. If the reward is prestige, money, software, a job offer, a volunteering offer/internship, name in game credits, or university transcript credit- make sure you communicate as clearly as possible otherwise you set yourself up to lose out every time.
The duration of the comittment you are offering must also be clear: would this be permanant, a contract position, one project, or several?
Location and region restrictions-
I don't know much about your company and structure but if you are looking specifically for artists only within your one country make sure that is stated very clearly.
If your local candidate pool is very small, you might consider doing a virtual position for your artist. Provided you have stable internet, there are more ways than ever to facilitate great communication and virtual team work including many free methods. If the phone is an option, hey this was done in the past in other fields and even today in areas with poor internet.
Where to "advertise"-
If you feel the contest is the best method you probably want to start where artists looking for employment "hang out." Check community artist forums in your primary language/country where you are located if that is most important. Post on places like cgsociety, conceptart.org, (maybe deviantart, it is less likely to find pros though) and the others. Indie game forums (if that is what your company is), game engine forums (how are you making this game? Unity for example has a job offer forum), and if you have social network accounts that already have a following can be a great place to start as well.
If you are just looking for a web platform to do this on, you may not need one beyond where you post ads and make people aware.
Artists these days often hang out on facebook, tumblr, lots of art websites, twitter, pinterest, stumbleupon. But you also probably want to ensure that you know your audience. Some of these sites will attract people who have never worked as professional artists, do not have the qualifications for what you may need, may not be able to do the work for a variety of reasons, may be way too young to offer employment despite how skilled they are, or may only be looking to challenge themselves.
It can sometimes open the floodgates especially if what you are requiring for the contest is not a lot of dedication, comitment, quality, and work.
You will need to decide based on your rules and who enters if anyone truly fits. Do not guarentee employment to the "winner" - make sure you offer them some kind of compensation, but safeguard yourself.
You want to make sure you get a chance to see other works your artist has made, that they can communicate clearly, availible, and will be pleasant enough to work with.
Company website-
I recomend using your company's official website if you have one, if not consider getting one- even if it is a blog format. You at minimum probably want to comit to a couple posts a year but sometimes more activity can draw more people in to follow your work.
Mostly you'd just want a domain unless that is out of the budget (website domains are pretty inexpensive- about 10$ a year for a .com). Hosting in general is significantly more (tiny companies might get by with small hosting packages, more popular ones might need bigger packages- this could be around $100 USD to thousands depending on your level of traffic), and if budget is super tight you might consider just using something like tumblr.com, blogger, or a free wordpress site.
Then using the domain and a clean layout to add to the professional sense. Even if you are a fun and quirky company you still want to be professional as a business, otherwise it will be much harder for serious artists to take you as legitimate work. In all honesty you probably don't want ads on your website if you can help it, unless they are for your own products/games/contests/etc.
Special note-
You probably want to maintain a type of "master list" for your rules. One great way to do this can be a read only/but availible to the public document like a google docs page.
However if you choose to copy and paste your contest rules on multiple websites, remember any time you need to make a change or clarification, or fix a problem that you will set yourself up for a lot of extra work. If you don't have the time to maintain that- (and trust me that can happen rather quickly), be sure to try to make changes only one time in one place if you can.
If not, make changes to a master contest post that you can then copy and paste easily in other places. You definately don't want a situation where you update every single place you posted individually manually each time and possibly leave things out, wreck the document, etc.
You probably also want some type of branding to your contest/company so it feels official and more special to just you as a company- not whatever websites you post on. Maintain a degree of professionalism in the look, quality of the contest's documentation, and "branding" with logos, your company's name, what your past or current work is, etc. Also consider giving some idea of what your culture as a group or company is so the artist can know if they will not fit in. Branding and how you present information can help clarify that.
Personally if a document isn't readable to me and I'm confused as to what you want- I would just walk away. You don't need to format to perfection, but make sure most people can read it and know what your "ad" is all about!
Additional considerations-
You want to make sure you are also hiring a good fit temperment and culture wise to your team. Make sure that the art test is not the only part of your "interview" or you may end up with an artist who won't work out. You want to test their creativity, technical skills, ability to follow directions, work under a deadline, and potentially how they accept feedback. This is pretty traditional for an art test, it is just being offered publically to multiple people at once and up front- rather than after another part of an interview and in private, one at a time.
Artists want stability, compensation, clarity, and good treatment in addition to the creative component. Many people forget that artists require these things like everyone else and think that the creative and artistic oppertunity are "enough" to offer us. Being challenged and artistically fufilled is great but if we won't be able to pay our bills for a while and can't see how an offer will eventually help us to do that, it is often much harder for us to accept such an offer. So if compensation of some kind is something you can offer- make sure you emphasize this clearly.
Competitions and job offers grab attention, but you have to "sell" yourself to the artist too.
I am sure you know this, but I post this information not just for you but to anyone who stumbles upon this thread. Good luck!
A contest can be a way of promoting an open call art test of sorts. However make sure you make the rules to your context exceptionally clear for what you are looking for, and what the rewards are.
Rules-
What exactly you want for the contest. Be specific about what you are looking for technically, quality, and style wise. If you provide examples of some kind of what you are looking for. Try to offer some rules for the uniformity you require in order to judge- judging on creativity alone has it's time and place but in a situation like this I would want to feel comfortable with knowing what my judges were looking for.
If you do this via the internet as widely as possible, be aware you may need to set a minimum age for those who enter for legal reasons.
If you ask for a concept to be made of a character (or environment, item, etc.), provide an average amount of information you would provide to this artist in the job so they know what to expect.
If you are looking for something more "advanced" in the pipeline like 3D art, make sure you provide enough so you can reasonably expect to get what you are looking for from most entries.
Position-
What type of artist you are looking for and the expectations you have for the type of art. Depending on the type of art some art categories are more combined and would expect overlap, others may view them as more seperate (environment/character/concept splits for example, or a generalist/multi-discipline).
Rewards-
If this is a job and will result in pay and benefits make sure that is clear, because most artists will decline work where the "payment" is ambiguous. If the reward is prestige, money, software, a job offer, a volunteering offer/internship, name in game credits, or university transcript credit- make sure you communicate as clearly as possible otherwise you set yourself up to lose out every time.
The duration of the comittment you are offering must also be clear: would this be permanant, a contract position, one project, or several?
Location and region restrictions-
I don't know much about your company and structure but if you are looking specifically for artists only within your one country make sure that is stated very clearly.
If your local candidate pool is very small, you might consider doing a virtual position for your artist. Provided you have stable internet, there are more ways than ever to facilitate great communication and virtual team work including many free methods. If the phone is an option, hey this was done in the past in other fields and even today in areas with poor internet.
Where to "advertise"-
If you feel the contest is the best method you probably want to start where artists looking for employment "hang out." Check community artist forums in your primary language/country where you are located if that is most important. Post on places like cgsociety, conceptart.org, (maybe deviantart, it is less likely to find pros though) and the others. Indie game forums (if that is what your company is), game engine forums (how are you making this game? Unity for example has a job offer forum), and if you have social network accounts that already have a following can be a great place to start as well.
If you are just looking for a web platform to do this on, you may not need one beyond where you post ads and make people aware.
Artists these days often hang out on facebook, tumblr, lots of art websites, twitter, pinterest, stumbleupon. But you also probably want to ensure that you know your audience. Some of these sites will attract people who have never worked as professional artists, do not have the qualifications for what you may need, may not be able to do the work for a variety of reasons, may be way too young to offer employment despite how skilled they are, or may only be looking to challenge themselves.
It can sometimes open the floodgates especially if what you are requiring for the contest is not a lot of dedication, comitment, quality, and work.
You will need to decide based on your rules and who enters if anyone truly fits. Do not guarentee employment to the "winner" - make sure you offer them some kind of compensation, but safeguard yourself.
You want to make sure you get a chance to see other works your artist has made, that they can communicate clearly, availible, and will be pleasant enough to work with.
Company website-
I recomend using your company's official website if you have one, if not consider getting one- even if it is a blog format. You at minimum probably want to comit to a couple posts a year but sometimes more activity can draw more people in to follow your work.
Mostly you'd just want a domain unless that is out of the budget (website domains are pretty inexpensive- about 10$ a year for a .com). Hosting in general is significantly more (tiny companies might get by with small hosting packages, more popular ones might need bigger packages- this could be around $100 USD to thousands depending on your level of traffic), and if budget is super tight you might consider just using something like tumblr.com, blogger, or a free wordpress site.
Then using the domain and a clean layout to add to the professional sense. Even if you are a fun and quirky company you still want to be professional as a business, otherwise it will be much harder for serious artists to take you as legitimate work. In all honesty you probably don't want ads on your website if you can help it, unless they are for your own products/games/contests/etc.
Special note-
You probably want to maintain a type of "master list" for your rules. One great way to do this can be a read only/but availible to the public document like a google docs page.
However if you choose to copy and paste your contest rules on multiple websites, remember any time you need to make a change or clarification, or fix a problem that you will set yourself up for a lot of extra work. If you don't have the time to maintain that- (and trust me that can happen rather quickly), be sure to try to make changes only one time in one place if you can.
If not, make changes to a master contest post that you can then copy and paste easily in other places. You definately don't want a situation where you update every single place you posted individually manually each time and possibly leave things out, wreck the document, etc.
You probably also want some type of branding to your contest/company so it feels official and more special to just you as a company- not whatever websites you post on. Maintain a degree of professionalism in the look, quality of the contest's documentation, and "branding" with logos, your company's name, what your past or current work is, etc. Also consider giving some idea of what your culture as a group or company is so the artist can know if they will not fit in. Branding and how you present information can help clarify that.
Personally if a document isn't readable to me and I'm confused as to what you want- I would just walk away. You don't need to format to perfection, but make sure most people can read it and know what your "ad" is all about!
Additional considerations-
You want to make sure you are also hiring a good fit temperment and culture wise to your team. Make sure that the art test is not the only part of your "interview" or you may end up with an artist who won't work out. You want to test their creativity, technical skills, ability to follow directions, work under a deadline, and potentially how they accept feedback. This is pretty traditional for an art test, it is just being offered publically to multiple people at once and up front- rather than after another part of an interview and in private, one at a time.
Artists want stability, compensation, clarity, and good treatment in addition to the creative component. Many people forget that artists require these things like everyone else and think that the creative and artistic oppertunity are "enough" to offer us. Being challenged and artistically fufilled is great but if we won't be able to pay our bills for a while and can't see how an offer will eventually help us to do that, it is often much harder for us to accept such an offer. So if compensation of some kind is something you can offer- make sure you emphasize this clearly.
Competitions and job offers grab attention, but you have to "sell" yourself to the artist too.
I am sure you know this, but I post this information not just for you but to anyone who stumbles upon this thread. Good luck!