Most of my interaction with runners is on Twitter. Of the 1700 followers I have there, I would guess over 1000 are runners from all over the world. Every Sunday evening, we have a chat together called #runchat. What I have found out about most runners is that they don't discuss religion or politics, which is refreshing on social media. They are also good people. It makes sense. People that are attempting to live a healthy, fit life have a self discipline that spills over onto the other parts of their lives. Like you say, there are other communities. My wife is involved with quilters. I have seen the AT hiker community interact on Twitter and I follow the official AT group.