If you met me we would strike up a conversation until we hit common ground. That would be the platform from which we build our relationship.
Members in your community already have that common ground, it’s the topic of your community. You need to strengthen and grow this common ground. This bonds your community and increases repeat visits, decreases members leaving and stimulates more activity.
Your role then is to identify the common ground within the common ground. Spot what things members have in common beyond simply an interest in your topic. It might be 5 are from Cincinnati, or were ex-marines or are interested in a specific aspect of the topic.
Create forums, groups and pages for these people and issues. If you have 20 members who are dedicated Manchester United fans, create a special Manchester United group, badge, tag or forum for them. Appoint members to be in charge of this.
Spend as much time as you can doing this. It creates the sub groups which really drive a community.
This is easily one of the most overlooked elements in developing online communities.