Social Media News Ticker: Facebook Tests ‘Buy’ Button, Twitter Acquires CardSpring

Check out all the latest social media news from the last two weeks, including changes and new features for Facebook, Twitter, Foursquare, Tumblr, YouTube and Vine:

Facebook Mentions app

Facebook

Twitter

Foursquare

Tumblr

YouTube

Any social media updates that we missed? Let us know in the comments below.