Ning is the only online service where you can create, customize, and share your own Social Network for free in seconds. Ning.com allows anyone to easily create, through a drag and drop process, a Social Network on which members can post discussion items, blogs, photos and videos, and more. It is entirely free, with advertising, and $19/month without ads.

Founded in October 2004 to give everyone the opportunity to create social networks. Two and a half years later, Ning powers over 80,000 social networks and counting.

Although it is in no way only for health, there were close to 400+  social networks that are tagged “health”.