Instagram, which is just two years old, went from 886,000 daily mobile users in March to 4,589,000 in June and 7,302,000 in August, a nearly 8.5-fold increase, according to comScore, an online tracking and analytics firm.

Twitter had 6,868,000 daily active mobile users in August, up 24% over the same six month period. comScore said.

While comScore didn't include the number of daily mobile Facebook users, a spokesman said the social network has far more mobile users than Instagram and Twitter.

"I'd say Instagram has really benefitted by being ," said Zeus Kerravala, an analyst with ZK Research.

"People love to share photos but Facebook raised Instagram's profile. Social media junkies might have known about them but the general public's awareness of Instagram was low pre-Facebook," he added.