It won’t happen…at least not at the beginning.
When was the last time you reached out to friends and invited them to join any of the communities of which you’re a member?
I’m betting it wasn’t recently (if ever).
People don’t invite friends to join communities because they don’t want to put their credibility on the line. If you think you can invite the first few members and then your community will organically grow, you’re going to be extremely disappointed.
There are two things to understand here.
First, people don’t invite friends to join communities, they share content within those communities with their friends.
If you want viral growth your community has to be filled with content which is so interesting, valuable, and unique that members will be eager to share it. And the bar for this is very high indeed.
Second, relying on viral growth for success is a terrible strategy. A better approach is to identify how many people you can reach (existing names in your database), how many you can divert from existing traffic flows (your website etc..) and estimate the conversion rate. Then see how you can increase the conversion rates of both while getting people to stick around.
To rely on viral growth is to rely on chance. Don’t do it.