There are already some sizable facebook groups for flashlight purposes. Facebook works reasonably well for buying and selling items, as a way to advertise, and as a way to post glamour shots of new lights. It has replaced CPF Marketplace entirely. But due to the way facebook is structured, it doesn’t work very well for substantial discussions or projects. Threads generally don’t last more than a few days at most. Interaction there tends to be relatively shallow.
Also, due to the site’s “real names” policy, it’s hard to tell who anyone is because people aren’t allowed to use the names everyone knows them as.
Anyway, to get people interested, it may help to explain more about the group’s purpose. What is it about and how is it unique? What would draw someone to this group instead of one of the more established groups, like Flashlight Fanatics or Lumen Addicts?