You aren't going to be able start a Social Networking site with a CMS platform and a programming language. You need original design, a business plan, research into the demographic you will target and much, much more. Have you even bothered to read up on the work done to start Twitter, Facebook, LinkedIn, Reddit, or any of the other Social Media Sites.
Take some time and do some research of your own and then come back here and post specific questions to the appropriate forum(s) for them. This isn't the one. This forum is about Content for Social Media, not about development of Social Media Sites.