Here is a report about the top networking sites as of March, 2013. It is a good idea to keep an eye on trends. Things can change quickly. I was surprised to see My Space rank so high. I didn’t know anybody still used that site. Last time I visited, it was so cluttered. Will have to take another look. Maybe they have redesigned it.
Maximize Your Promotional Time: A Report on Most Popular Social Networking Sites
One Way to Wonder 
Very interesting! I’m not at all surprised by the first 4 listed here, and now knowing the other 11 popular sites I can better gauge what I follow and and choose to learn more about for my clients.
Thanks, Stephanie!