Facebook acquired mobile messaging app, WhatsApp on February 19, 2014 for $19 billion. The app is an alternative to SMS which allows users to send messages for free across smartphone platforms. More than 450 million people use the app every day.
Facebook also acquired the photo-sharing app, Instagram for $1 billion in April 2012. The app has 150 million active users.
Twitter bought Vine, a 6-second video clip application, for $30 million in October 2012. As of January 2014, the app has 40 million registered users.
Yahoo purchased the popular blogging service, Tumblr, for about $1.1 billion in May 2013. Currently, there are 172.5 million blogs and 77.4 billion posts on the site.