What is the newest Social Network that you will recommend for us to sign up with ?

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When I first participate in those Social Network such as MY Space, Facebook, Stumbleupon, Twitter and etc. I though it was pretty fun. Then there came Pinterest and many more. I started to getting confused with all these Social Networks.It was fun in the beginning but it would take lots of time to develop it if you really wanted to build some targeted traffic with it. I just don't have time to do it, so I don't us it often right now. Anyway, I still remain open if there are some good Social Network comes up and maybe you can tell me some of this newest website I can participate and at least to have fun with it. Share with us ?