I found a niche social network for internet marketers and that is Masti On Web at http://www.mastionweb.com/ SEO, SMO community. 1st 15 Members will be Sen. Moderator next 15 will be Moderator. and They will get 1 crore Points, are you ready???
Businesses have adapted their means of communication and ways of doing to accommodate social media interaction. It is used as a tool to get in touch with consumers via the internet; knowing that the internet is a powerful and definitive electronic venue for public gathering.
Social Networks come and go for almost every niche, I have joined may SEO one before only to see them disappear a few weeks later, always better to build communities on twitter followers in lists and Google+ circles etc if you want them to provide value long term.
There are really various social networking sites which are good for internet marketing. The main task is to manage all the accounts in a proper way simultaneously. You can use sociaoboard for this purpose, it is a goof social media management tool.