You can't launch a community with a 'seeing what sticks' approach.
This usually means mass-mailing everyone on your lists, securing some media coverage and hoping for a high conversion rate, like 20%.
You can't do this because people aren't mud.
They don’t stick or slide waiting to be thrown around. If they visit the community and don't like it, they bounce. It’s much harder to get them back for a second look.
If you have to use a metaphor, try this. People are balls. Your community is a hole (oh dear). Your job is to guide every available ball into the hole. If any bounce or miss, you’ve made your job harder.
Have a soft launch. Grow slowly and deliberately. Cater to one group at a time, invite select people in batches.