Instagram on Tuesday said it had passed a milestone, with its community having grown to more than 500 million members -- more than 300 million of them using the site on a daily basis. The Instagram community has become more global, with more than 80 percent of Instagrammers living outside the United States. Instagram's user base has more than doubled in two years, surging past rival photo-sharing site Snapchat. Its growth spurt comes at a time when Twitter growth appears to be stagnating as it struggles for profitability.