Tumblr: David Karp's $800 Million Art Project - Forbes
: "Tumblr’s tens of millions of registered users create 120,000 new blogs every day, for a total of 86 million and counting, which drive some 18 billion page views per month. Its latest funding round, in September 2011, valued Tumblr at $800 million, making Karp’s 25%-plus stake worth more than $200 million. Then its traffic doubled."
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