Ask your members what they're doing this weekend.
People love to talk about themselves. Self-disclosure is important in online communities. Other people might be nearby or doing something similar (meet-up potential). Members will return to see what other people have said about their weekends. When they do that they might reply to others – it encourages them to return too. It becomes a beneficial cycle.
All the time this is happening, your community is developing.
In addition, next week, you can reference the activities that people have done. You can ask them how it went. If anyone mentions anything especially interesting, you can mention it in a news post.
Community building can be quite simple.
