There are successful and unsuccessful social networks. Successful social networks are social and fun: http://www.zengestrom.com/blog/2005/04/why-some-social-network-services-work-and-others-dont-or-the-case-for-object-centered-sociality.html
Discussion
The success of a social network with a physical or digital presence should always be focused on your group of humans with whom you want to share things in common. Today they have all forgotten.