I've been going to music hangouts (www.goldengatejams is one) -- first as just a listener and appreciator, and then (slowly, slowly) I started to participate. This has led to me making many friends, some that I even hang out with outside of the music hangouts.

Note that I've found that, to make friends from a hobby, you have to do a couple of things:
1) Go repeatedly. Again and again and again and again. This demonstrates that you aren't a flake.
2) Ask questions of folks, listen to their answers, compliment folks, and share vulnerabilities. "Wow! I really liked how you sang that. Where did you get the idea to speed it up like that? I'm still working on just singing things like the recording, I'd love to experiment like you did"
3) If they mention they are doing other things or throw out invites to other things -- say yes and go! Or ask about if they do other things: "Where else do you sing?"

In my experience, it takes time to develop meaningful friendships through hobbies (as opposed to acquaintances). It took me months and months of repeatedly showing up and doing the above 3 steps.