Identify and create your community advocates across multiple channels. These folks will be responsible to create a buzz about your community and help bring in new users by leveraging their network.
Identify who are the top contributors each month consistently. Promote them to become community volunteers to help you run the community.
Referral campaigns are the best way to attract new users to the community. Create a leaderboard of the referral campaign to make it a gamified experience.
Collaborate with folks who are influential in the community space, who understand and talk about the problem you are trying to solve. Partner with other community towards a greater vision.