After the acquisition by Yahoo I wanted to know about Tumblr.
Tumblr, stylized in their logo as tumblr., is a microblogging platform and social networking website, owned and operated by Tumblr, Inc. The service allows users to post multimedia and other content to a short-form blog.
Users can follow other users' blogs, as well as make their blogs private. Much of the website's features are accessed from the "dashboard" interface, where the option to post content and posts of followed blogs appear. Its headquarters is in New York. It was founded in February 2007.
As of May 19, 2013, Tumblr hosts over 108.2 million blogs and more than 50.8 billion posts in total.
In April 2013 the website received more than 13 billion global page views. As of May 2013, 75.8 million posts were created on the site each day.
The service is most popular with the teen and college-aged user segments with half of Tumblr's visitor base being under the age of 25.
I found only one leading Indian brand on it.