Who is using facebook?
In June 2013 facebook had 1.26 billion users (accounts) which is nearly 10% of the worlds population, of this 24 million Britain’s actively use facebook everyday, that’s about 15% of the British population!
https://www.facebook.com/notes/facebook-data-science/whats-on-your-mind/477517358858
http://expandedramblings.com/index.php/by-the-numbers-17-amazing-facebook-stats/#.UqI2UtJdWSo
http://www.technologyreview.com/featuredstory/428150/what-facebook-knows/