A Facebook page is the way to go, however uniform and conformist it may appear. People are on there all the time and will get used to taking a look at what is going on and then hopefully join. The question is how you set it up - do you go public and have it monitored against the foodies, the general cranks and the non-member or do you go private which keeps it in-house but has less exposure. We have a private one for the Fungal Friends Group and the members use it regularly. I am not a Facebook fan but it is a necessary evil when pushing walks and gigs.
Cheers
FP Dave