Facebook is currently the number one social media network in terms of number of users, daily users, and daily activity. At the same time, it has been designed for casual network, unlike Twitter and LinkedIn which is more of a more professional nature. Because of this diversity, the demographics are off the chart.
Below is an infographic of who is using Facebook, who their friends are, and what they are doing on their.
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The highlights: while people may be on Facebook daily, they are not necessarily updating information all the time.