I recently listened to a Mixergy interview with Seth Godin about communities and tribes. Below are of a few great concepts that stood out.
Building a community involves creating a place where people can connect with one another. However, the community must also have a purpose, and you must communicate that core mission to your tribe. The tribe is simply a tactic to drive change. Our mission is to provide you with professional feedback, and the greater purpose is to ensure innovative ideas are executed successfully.