Tumblr Surpasses 13 Million Monthly Unique Visitors In U.S.

Blogging service Tumblr on Tuesday announced a new record number of unique visitors for a single month. According to site officials Tumblr scored 13.4 million unique visitors in the U.S. during the month of July.

If those numbers are correct that would mean a 218% increase in site visitors based on the same period one year earlier.

Analytic information firm comScore also shows that Tumblr has seen their most massive increase since inception from April to July where visitor counts increased by more than 5 million monthly uniques.

comScore’s Andrew Lipsman told Mashable that the sites increases is thanks in large part to a mass appeal effect:

“The network effect is predicated on the idea that the more users that are part of the system, the more valuable the system becomes to users, which creates a virtuous cycle that pulls more users into the system and gives existing users more incentive to participate,” while he went on to add, “This concept is an important reason why we often see that once social networks achieve critical mass, the network effect takes hold and adoption tends to accelerate.”

Since being founded in 2007 Tumblr has managed to attract more than 20 million blogs as of June 2011 with more than 28 millions blogs now online.

In the meantime Tumblr is said to be seeking out investors so they can raise somewhere in the vicinity of $75 million to $100 million in funding, enough money to valuate the company in the area of $1 billion.

Here’s a chart showing Tumblr visitor growth: