I administer a FB page for our local trail running club the
Shenipsit Striders. A couple years ago our club membership was dwindling to near zero and we almost folded (or more appropriately merged with a road running club). Opted to make one more run at it and engage social media - a FB page was our choice.
We post a variety of notices etc to the page, but the primary function that has drawn in new blood has been to post training runs. Most of our core members are going out for trail runs regularly anyway, so we encouraged them to post the time & place (and pace if appropriate) and encourage others to join them. Running with a group also helps to motivate and maintain commitment to the training. And if no one shows, its no biggie, because you were going to go run anyway, right? But the more the merrier...
The problem that arises is that people have to visit the page to see member posts, whereas posts by administrators (ie me), get posted to each members wall. So when someone posts a training run, I generally repost (as admin), add it to the google calendar (included on our
regular web page), and delete the original posting (unless others have already commented on it).
So what used to be just solo training runs now generally draw 4-15 people on average. Big groups can break into slow/fast groups etc. And we've been getting a variety of folks coming out to these runs - its not always the same dozen core members, but the 'leaders' of the runs tend to be regular members.
Some of these folks have gone on to join the club outright, but we're also fine with folks just getting out and socializing in the woods together, they don't have to join the club.
Another thing I do for runs I partake in, is to bring my camera and take a group shot before or after the run and post it to the FB page and have folks tag it. This helps break the ice for newcomers who have never run with us - they can see that we're not a bunch of scary looking deviants (or conversely, perhaps that we are a scary looking bunch of deviants...) But it does lead to newcomers coming to a run and coming right up to folks the recognize from the FB photos and introducing themselves. And it goes from there...