How to get maximum horizontal connections in a small community?

Question

Social media

Programmers are writing a new social network... it probably looks ridiculous, but there is such a word "SHOULD". And now it's time to ask stupid questions. Sociologists, tell me?
The network is a group with one common interest - motorcycles. There will not be millions of users here, but a couple of tens of thousands can be found. The portrait of the average user is 30 years old, male, as open as possible to "ours" and usually closed to "strangers". He earns enough, the "small penis" complex is not developed. "Their" are mostly the same.
In large Facebooks with connections, everything is clear, the development of the network is purely extensive: a million users gives ten million connections. But what about small (within the framework adopted in social networks) groups with one common hobby? What to offer users so interesting that they grow their connections and social capital?
I am a complete teapot in sociology, I do not understand anything in it at all, but for the sake of applied application I have no opportunity to study it fundamentally. Please put me on the right path :)