Instagram, the free photo sharing program launched in October 2010, has grown in popularity and shows no signs of cooling off any time soon.

With its distinctive features, similar to old-school Polaroid pictures, Instagram boasts nearly 50 million users and is currently growing at a rate of about 5 million per week, according to Mashable.

The rapid rate of growth is due to its largest acquisition deal to date, with Facebook snagging the company for approximately $1 billion in cash and stock in April 2012.

The photo sharing app, which is supported on iPhone, iPad, and iPod Touch and Android camera phones, is only two years old and is said to have unlimited potential, now that it's officially part of the Facebook repertoire.

Newbies to Instagram can sign up, login and take advantage of the Instagram Support center for great tips on how to use the service and more importantly, how to find the right Instagram users to follow.

The photo application, which lets users interact with Facebook and/or Twitter friends, has a Suggested Users tab -- the next best thing when discovering some of Instagram's most relative users.

One of the most popular features of Instagram is its Notable Users Directory. New members can use the directory to view some of the top users posting photos related to fashion, food, music, news, and more.

While the whole idea of Instagram is to post attractive pictures to the sharing site, IBTimes has compiled a list of the 10 most-followed users on Instagram. Celebs like Justin Bieber and Kim Kardashian are among the most popular.

Click Start to view some of Instagram's most popular celebrity users