Instagram has reached a milestone of 700 million members while enjoying the fastest-ever growth rate in the company’s history. The network has grown by more than 100 million members in the last four months. Its burgeoning growth can be credited to new features like Stories, live video and disappearing messages in Direct, the company said. “Ostensibly copied from Snapchat, the feature was significant in driving the ephemeral messaging app to an IPO,” said Zach Fuller, an analyst at Midia Research.