Which comes first, the platform or the people?
Do you build a spectacular place for people to hang out, get information, talk to each other, buy things, and then invite them in?
Or do you build excitement within a tight group of people with a specific common interest and then create a place for them to gather?
Unless you enjoy frustration, the second answer is correct. It's exceedingly difficult to begin a community from a "cold start." Don't get me wrong, technology is cool and all, but only in service to the humans who need it. If you have no humans, you have no community.
A further note for aspiring community-builders: it really helps if you are part of the tight group of people, rather than an outside force trying to artificially start something.
For reference, take a second look at our interview with Morgan Luce of Vermont Farm & Garden. She did it right, and a year later, her community is thriving! (She's got the chickens and the eggs.)
Image via Flickr CC: LollyKnit