If you know what platform you'd like to deliver it on, find forums, IRC channels, etc. for that platform? Lining up artists and marketing might help you attract a developer as well ("I have an idea, make it for me" tends to get dismissed).
As others pointed out already, gaming sites and forums get many requests of this kind, without some proof that you are serious about the project they won't care about it (though will most likely give some general advice that's helpful.) A less specialized site to post would be reddit in some of the gaming oriented subreddits like http://www.reddit.com/r/gamedev/