and I guess that the vast bulk of mobile games earn ZERO, webgames are a bit better it seems. The apple and google stores (and increasingly windows) are so large that most apps will never be listed in the top100. so it's not really fair to ask someone to contribute work (coders, artists, etc) with the illusion of future payments when there is little.
As someone else said.. put the effort in first.. show that you're credible, then you might get support.
alternatively be honest, and say it's a learning experience for everyone involved, it's for a good cause, or it's just you and your friends.
PS: I look around elance. the price of hiring a piece of work to be done is relatively low. if you can't afford that.. then you probably can't afford to be in the game.