Great question.
There's no magic bullet, but here are some bullet points for what has helped us over the years:
1) Be authentic to your product and your company. Share, and repeat that authentic voice wherever you can.
2) Identify patterns in your "high usage" members and encourage all members to do the same.
3) Don't bend to every request of the customer; be confident in what you're delivering, establishing yourself as a thought leader.
4) Try to drive any and all communication with your members through the channels you're targeting. For example, if someone emails you a support question, re-paste it in your community (along with your response) and respond to the requester individually telling them their answer is at the URL.
5) Communicate transparently in terms of what your intentions are with the marketplace and what you're doing to improve it.
It's tough without knowing more about your specific market place. Happy to chat to get more in-depth.
