After launching three communities over the past two years, here's what I've learned about the critical first 100 members:

1. Seed the content yourself. Nobody wants to post in an empty forum. Write 10–15 quality topics across different spaces before inviting anyone.
2. Personal invitations beat mass emails. Send individual messages to people you know will contribute.
3. Respond to everything. For the first month, reply to every single post. People come back when they feel heard.
4. Celebrate first-time posters. A simple "Great first post, welcome!" goes a long way.

The goal isn't growth — it's establishing the culture. Get the first 100 right and the next 1,000 takes care of itself.