Hi, I guess ranking of Social Networking Site may depends on the location and the user itself. Anyway, here's my top 5 SNS 1. Facebook 2. Twitter 3. Google + 4. Instagram 5. LinkedIn
Facebook Google + Twitter LinkedIn Tumblr I've seen YouTube in some lists. Though I use it, I don't consider it a social network
It doesn't seem like Tumblr is getting a lot of love. They and Pinterest are by far the fastest growing Social Media sites currently. I'll say in terms of Users V Rewards 1. Facebook 2. Linked In 3. Google + (Also because it's connected with Youtube as well) 4. Pinterest 5. Tumblr