Instagram opened its platform to a couple of hundred advertisers in June, the company said, and by September had opened the app to anyone wanting to purchase an ad. Three-quarters of its advertisers are now outside of the United States, the company said.
               
Instagram has also rapidly grown its user base, surpassing 400 million users last year. By comparison, Twitter, which began selling advertisements more than five years ago, has 130,000 advertisers and 320 million users.

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Instagram has had distinct advantages: It uses Facebook's ad technology, which is among the most advanced and allows advertisers to target highly specific demographic groups, such as 18-25 year old males who live in New York. And advertisers have the option to run campaigns across both Facebook and Instagram.