Social Media is about being social. But before you say, "Duh," let me ask you to think about what the term social means to you.
As a writer, I'm always concerned about defining terms. It's my belief that you can't have a real conversation with someone until you understand the thinking behind the lexicon.
To me, social means give and take - a conversation. On a lot of small nonprofit sites and social media accounts, though, what I see happening is a lot of me, me, me. Information about what the NP is doing, planning to do, hoping to do for the community, but not a lot about what the community itself is doing. Not a lot of interaction except from the viewpoint of the NP.
Posting information doesn't give your community anything to work with. To be engaged, involved, caring, they need a way to talk about your mission, explore your choices with you. Maybe that isn't possible on your website because you just don't have the resources - and it does take time and care to grow and maintain a community - but that doesn't mean you have to give up.
Instead of hoping the community will come to you, you can go out and find them. On Facebook, on Twitter, on Friendfeed, on Ning or on someone's blog. Find out where the conversations related to your mission are happening and interact: respond, encourage, help with tips and links. Add community links to your website and do everything you can to keep the conversations going. And keep at it. Social media is about trust - that your interaction is about the mission being served and not a marketing ploy - it will take time to gain trust, but once you do, the horizon will open up. The encouragement, support, and assistance you provide will come back to you in larger measure than you could have imagined.