Given that Instagram is only on one platform, and that too, a platform that is exclusive to very few devices, it's a wonder that the app could be the biggest mobile only social network. Yet, the app has crossed 25 million users and achieved the status described, earlier. No doubt, Instagram has been around for a long time (since October of 2010) and over that course of time, the Android-based competition has included apps like Picplz and more recently, Lightbox. According to a post on the blog, Lies, Damn Lies and Statistics by head of UK-based social media agency, Rabbit, Instagram has passed 25 million users, while Foursquare, a multi-platform mobile and somewhat desktop application is at 22 million users. These numbers come from two web viewers who also use the Instagram API. A web viewer is a site that allows people to see Instagram photos on their desktops or through their mobile browsers. The two viewers that revealed Instagram numbers were Statigram and Ink361. Statigram requires you to be an Instagram user for use.
Taking over mobile devices everywhere
On Statigram, when you view an Instagrammer's profile in the URL, you can see the Instagram user number of the person whose profile you're viewing. For instance, Kevin Systrom, the founder of Instagram, is listed as 3, which means he must have been the third person to join Instagram. Now, Rabbit found a user, @holliejsmith whose Instagram number is 25,973,449 on both Instagram viewers, which means that Instagram is close to having 26 million users. Using the same process, Rabbit found Foursquare to have 22 million users. The problem with using this method, as stated by The Next Web, is that it isn't entirely accurate. There aren't any number one or number two accounts (straight to number three), and many accounts may just be test accounts.
Instagram claimed to have 16 million users in December and given that many people gift iOS devices around the holiday season, the number of users may have dramatically jumped, indeed. Furthermore, Instagram is preparing an Android application as well, which may play a role in boosting numbers further in the near future.