Instagram has really taken off over the past year, with user growth accelerating while the Facebook (NASDAQ:FB) subsidiary continues to add more and more features to the already popular photo- and video-sharing service. That includes everything from new e-commerce features to the recent launch of IGTV, a long-form video content platform. At least one Street analyst is modeling for Instagram to generate nearly $9 billion in revenue this year.

In a stunning new estimate released yesterday, Instagram could be worth $100 billion -- representing over a sixth of Facebook's current market cap (roughly $575 billion).

Instagram interface on iOS and Android

Image source: Instagram.

A 140-bagger

Bloomberg Intelligence is estimating that Instagram's valuation could be in 12-digit territory, which would represent a 100-fold return for Facebook after acquiring the fledgling service back in 2012 for $1 billion. In fact, the final price tag upon closing was actually lower, just $715 million, due to stock price fluctuations related to the stock portion of the deal, making Facebook's return even greater -- a nearly 140-fold return.

Bloomberg Intelligence analyst Jitendra Waral estimates that Instagram's revenue will exceed $10 billion at some point over the next year (presumably measured on a trailing-12-month basis). Waral is encouraged by the fact that Instagram's monthly active user (MAU) growth has been accelerating and is outpacing Facebook's core service, which has seen growth slow due in part to its sheer size. Facebook currently has 2.2 billion MAUs worldwide, while Instagram hit 1 billion last week.

For historical context, here's how the two services have grown their respective MAU bases over the years. Note that unlike Facebook, Instagram does not disclose MAU figures on a regular basis, but only announces when it hits certain milestones.

Chart comparing user bases of Facebook and Instagram

Data source: SEC filings and Instagram. Chart by author.

Waral believes that Instagram's MAU base could even overtake Facebook's within the next five years. Furthermore, the demographics of Instagram's user base skew younger, which is a lucrative audience for advertisers.

Not only has Facebook's MAU growth slowed recently, but essentially all of its MAU growth now comes from abroad -- markets that are harder for Facebook to monetize. It's become increasingly clear that its North American MAU base has peaked due to market saturation. The company added just 2 million MAUs in North America in the first quarter, where advertising average revenue per user (ARPU) is nearly three times greater than markets like Europe. Instagram does not disclose a geographical breakdown of its user base, but undoubtedly still has room to grow in the lucrative U.S. market.

With as important as Instagram is becoming to Facebook, both operationally and financially, it's about time for the social media giant to start disclosing Instagram metrics on the regular.

Evan Niu, CFA owns shares of Facebook. The Motley Fool owns shares of and recommends Facebook. The Motley Fool has a disclosure policy.