The Calhoun Beach Club used to have a running group. It was a good deal too b/c they would meet at the club and you could use the shower facilities and the running club rate. You didn't get to work out, etc. But the group seemed pretty committed. They usually did lake routes, but also did some interval training and running hills, marathon training, etc.
Another running group is the Running Room in Uptown.
I don't know of any 'gay' running groups.