This article was updated on April 26, 2017, and originally published on April 8, 2017.

When Facebook (NASDAQ:FB) began notifying users in 2014 that they wouldn't be able to message people through the mobile Facebook app anymore and would instead be forced to use the separate Facebook Messenger app, it raised more than a few eyebrows. But about three years later, it looks like the move has paid off for the company. Today, Facebook Messenger is the world's second-largest social network (tied with Facebook's WhatsApp messaging service).

How many users does Facebook Messenger have? 1.2 billion monthly active users, as of Facebook's last update on the messaging app.

Group of young people using laptops, tablets, and smartphones

How many users does Facebook Messenger have? Image source: Getty Images.

Facebook Messenger's rapid growth

It didn't take long for Messenger to grow to 1.2 billion monthly active users. Here's a look at Messenger's monthly active users on the various dates Facebook has shared an update on the service's size. 

Messenger Monthly Active Users

Date

500 million

November 2014

600 million

March 2015

700 million

June 2015

800 million

December 2015

900 million

April 2016

1 billion

July 2016

1.2 billion

April 2017

Data source: Facebook blog posts and quarterly updates. Chart by author.

The app is undoubtedly a hit, growing from 500 million monthly active users in 2014 to 1.2 billion in the first half of 2017.

It's also worth emphasizing that Messenger is rivaled by Facebook's own WhatsApp, a messaging app which the social network acquired in 2014. As of February, the service also had 1.2 billion monthly active users, putting it up there with Messenger and just behind Facebook's core social network app, which has just under 2 billion monthly active users.

A big bet

Thanks to Facebook's rapid deployment of new features on Messenger, the app has morphed into far more than a messaging service. It's increasingly turning into a comprehensive social network in and of itself, making it appealing even if it isn't used in conjunction with Facebook. Today, users can use the service for text, group, audio, and video messaging, as well as to share locations, send stickers, interact with businesses, buy products, request an Uber ride, and more.

Recently, Messenger has received even more attention from Facebook. Following Snap's initial public offering in March of 2017, Facebook debuted Snapchat's "stories" format -- which enables users to collect and share photos and videos for 24 hours before they disappear -- on Messenger. The move came as part of an all-out competitive assault on Snapchat that included bringing the stories format to Facebook. 

Time to monetize Messenger?

Of course, the next logical step for Facebook is to monetize Messenger. But investors shouldn't expect this to happen too quickly. In Facebook's fourth-quarter 2016 earnings call, CFO Sheryl Sandberg said the company is still primarily focused on "consumer growth and engagement." But investors shouldn't mistake this to mean that Facebook doesn't see monetization of Messenger on the horizon. Sandberg went on to say the reason it is so focused on user growth and engagement is that this is ultimately what will create monetization opportunities on Messenger.

Of course, while user growth and engagement are Facebook's primary focus right now, the company is already testing some ads on the platform. Sandberg admits, however, that Facebook is still in the "early stages" of exploring ads on the platform.

With Messenger's growth exploding since it was separated from the Facebook app, and with Facebook's WhatsApp and Messenger messaging services holding two of the top three spots in the world's largest social networks, messaging is clearly a key frontier for building out massive social networks today.

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Daniel Sparks owns shares of Facebook. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), and Facebook. The Motley Fool has a disclosure policy.