"Like instagram and pintrest have both succeeded. But I don't feel these 2 examples are good examples of community."

I completely agree with this. It goes back to what I used to speak a lot about when I worked at Threadless, which is a group of customers/users vs. a community. Thanks to Facebook (and OAuth in general), these days, early growth can be attributed to leveraging pre-existing social connections. I don't feel that knowing everyone ahead of time is a prerequisite for growing a strong community. A tightly connected social graph doesn't guarantee a great community (or a community at all), but building off of a tightly connected *interest graph* (read: common interests) like Pinterest/Behance/Quora/etc has a much better shot.