Selling venture capital shareholders include Accel Partners (selling 49 million shares in the offering), DST Global Limited (selling almost 45.7 million shares), Greylock Partners (7.6 million), Meritech Capital Partners (7 million) and Elevation Partners (4.6 million).
In addition, the size of the over-allotment option has been increased by 15.5 million shares, all of which are offered by the selling shareholders. The over-allotment option (also known as the Green Shoe) enable the underwriters to manage the post-IPO market price of the company, with the goal that the after-market price doesn't fall below (or "break") the original IPO price. In most successful IPOs where the stock price rises meaningfully after the IPO and stays that way for several trading days, the over-allotment option is fully exercised.
Link to amended registration statement: http://www.sec.gov/Archives/edgar/data/1326801/000119312512235588/d287954ds1a.htm#toc287954_6