Are you a non-technical person leading technical people?

If they don't share your vision and aren't getting paid you're not going to keep them around for long. People are often eager to help their friends but then regret what they've gotten themselves into when the task becomes too large.

You either need to find people as passionate about your idea as you, or offer them some compensation that they care about. There's no easy way to get good work out of people for free other than telling them they get college credit for it or that it's the only way to advance their career.