If your online community aims to connect two groups, you have a problem. Neither group will join until the other group is already there.
Buyers wont join a community en-masse if there are no sellers. Estate agencies wont join a community without house-hunters. Job-seekers wont join a community with no employers or recruitment agencies.
There are only two solutions to this.
1. Tiny Targeting. Target a tiny group with as much in common as possible. Perhaps people who live within one mile of each other. Or people looking/recruiting for one type of job e.g. community manager.
2. Ladies night.
Ladies night isn’t fair, but it worked. Women go because they get the best offers, men go because the women are there. The lesson is, don’t treat both groups equally.
Cater to one group more than the other. Give one group huge incentives to join. Give them great content. Invite VIPs to give live-chats. Have a brilliant FAQ wiki. Offer product discounts. Give them an inside communications channel to your client. Let them decide what they want to happen in the community.
Next open membership to the second group, but limit the number of people who can join. Don’t overwhelm your first group. Create a waiting list for people who want to join, and keep them updated in the meantime. Warn the people in the community they need to be active participators, you’ve got people waiting.