Please provide additional information about what kind of game you're working on. There are some types of games (i.e. NSFW) that not all artists may feel comfortable being associated with.
Also, how do you plan to compensate artists for their work? Is this a commission based project? Will you offer a percentage of the total profit from project sales? Or, are you paying in experience (looking for unpaid volunteers)?
I understand wanting to be secretive about what exactly your game is about, but you need to be clear about expectations when looking for people to work with