Experienced Python/SQL guy. Looking to collaborate, build, & channel my inner entrepreneur.

I work full-time as a software engineer for a company that I'm very happy with. I'd like to join a startup that is essentially in the extremely early phase of formation, so it could allow me to keep my full-time job, while contributing to the startup on weekends or nights. If the startup ends up getting traction, I'd be happy to join full time.

I guess what I'm after is an opportunity that would allow me to come in as one of the startup's core members, that would have me wearing many hats (technical & entrepreneurial). My dream would be to be one of the reasons a company was able to hit the ground running & be successful.

So I guess my question is what's the best way to go about networking to find these startups that are more or less in the concept phase? I don't want something that's a 9-5 (because I have that already). I want something that's someone's side project that I can contribute to in hopes of forming it into a living, breathing product.

Thanks!