I have talked to quite a few people who have a similar idea. The thing is facebook, linkedIn and Meetup already have a lot of this space covered along with several other less well known social networks. 

The question is what would I be looking for that I would want to find from an online network? I think people in the community, potential business partners investors and so on. But what I think would really work is information around running starts. So stories, webinars and so on. I think content would be primary, followed by the people.

The reason why I am suspicious about the people aspect is that anyone useful would be swamped by wannabe's trying to connect with them. But content would mean people at all levels would come to contribute and to share.

TradeSNS is a good platform for social network. You can make friends on it, find business partners. I think TradeSNS is very convenient.