It’s very difficult to get an unpaid team to work together. Realistically, you’d have to gain a large amount of experience to have any chance that people will work with you for free.
As far as ideas go, no one’s going to steal your idea since they very often have ideas of their own, which is also a problem when trying to build a team since people are more likely to want to work on their own projects if they’re going to put a lot of time into something.