Don’t try to restrict activity to your community website. Encourage as much activity elsewhere as you can.
Encourage members to meet up in their local towns and cities.
Encourage members to talk to each other on Twitter, e-mail each other and friend each other on Facebook.
Encourage members to e-mail each other and set up their own groups/places to chat about topics.
It’s sometimes hard to remember that the website isn’t your community, the people are. Fostering those interactions, wherever they may take place, brings your audience together.