Especially for a hobby project, a "team" is just formed out of people you are friendly with, and know relatively well. They also must be talented.
The Sky Sanctuary team is comprised primarily of people that the original devteam were friendly with, because as friends naturally go, "one conversation leads to doing favors, which leads to getting work done for the game." It kinda' happens naturally. You can also cherrypick talents for people you don't know, but in the end, both people will have to want to work with each other. It's the same way with getting a job.