Fear of missing out (FoMO) is now salient.
Every time you visit Facebook, Twitter, or your community site, you can see everything you're missing. That might be holidays, parties, events, speaking opportunities, and successes that some people gained…but not you.
This especially affects the young (notable young males), those in negative moods, lower life satisfaction, and lower needs satisfaction (autonomy, competence, and relatedness).
Now consider this. We have an innate need to impress our peers. We want to achieve a positive distinctiveness among our perceived peer group.
Therefore, we use our profiles to construct our ideal identities. We use our profiles to create the people we want to be (or the people we want our peers to think we are). We select the best picture, most interesting/positive information, and do everything we can to ensure our profiles reflect us in a light that will impress our peers.
Now combine these three elements; fear of missing out, ideal identity construction, and desire to impress others. This is a powerful force of nature to attract regular, repeat, visitors.
For better or worse, FoMO is an effective appeal to encourage people to visit and participate in communities. If you drop a few names of other members (within the peer group), mention a few events that people missed out on (especially social gatherings or speaking events), and highlight the success people within the group have achieved, you can increase the number of visits and participation.
Also read Seth's take.