This is a great object lesson in community development by experts at Flickr.

We very carefully built the community on Flickr, person by person. The team and I greeted every single person who arrived, introduced them around, hung out in the chatrooms.

It was a very hands-on process, building the community. And in the beginning Flickr was built side-by-side with feedback from the community: We were posting over 50 times a day in the forums. After you hit, say 10,000 members, or so, hopefully you’ve created a strong enough culture that people are greeting each other. It really is kind of like building a civilization.

Source:  CNET