Growth and Eventual Decline of Facebook.com
The black points plotted below represent the number of active Facebook users u, in millions, t months after December 2004. For example, in December 2005, there were about 5.5 million active users, so the point (12, 5.5) is shown. The data ends in April 2012. Also shown, in the form of three graphs, is the solution of an SIR infectious disease model. (See Wikipedia for details.)