There are lots of places here that need volunteers! I know that the Help the Animals shelter, where I work, is always looking for people to come in- usually interacting with the animals. It's probably not the place to be when you are looking to make human friends, I suppose! Museums usually need volunteers, as well as other non-profit organizations. One way to start is to think about your hobbies or things you like, and call up places in town that do that sort of thing. They might need help, or someone working there might know about groups you could join.
Nanette, Ariel has some great suggestions. Some other places I might suggest are Galileo, the Friends School, or really any of the schools - tutoring, helping with a club, etc.?
Boys and Girls Club and Girls, Inc. if you want to support our youngsters. You could also become a leader of a Boy Scouts or Girl Scouts regiment, and so on. There are a lot of ways to volunteer. I know you requested information some years ago, but hopefully this will still find you and be helpful