9. Tumblr (550 Million Users)
Next up at number nine is micro-blogging and social networking website Tumblr with 550 active million users. It was founded in 2007. It was founded by David Karp, who also serves as the CEO of the company. Tumblr enables users to post multimedia and other content into a shot-form blog. Users can also follow others user’s blogs. The website features are accessed from a dashboard interface for bloggers.