NEW YORK (TheStreet) -- Facebook's (FB - Get Report) WhatsApp platform has hit a new milestone with 900 million monthly active users. The messaging service added 100 million new subscribers in less than five months.

MAUs, or monthly active users, is a closely watched industry statistic for measuring the success rate of social networking services.WhatApp has gained popularity since Facebook acquired it in 2014 for $19 billion. In comparison,  parent company Facebook announced it has 1.49 billion monthly active users back in June -- a 13% year-over-year jump. The company also reported 1.31 billion mobile monthly active users in June, up 23% from June 2014.

WhatsApp is still ahead of the Facebook Messenger app, which currently has 700 million MAUs. But between them, Facebook has the world'stwo most popular messaging apps in its portfolio.

Menlo Park, Calif.-based Facebook is a social networking website company, with its applications enabling customers to stay connected with their friends and family. The company is engaged in developing products and offers various services focused on people, marketers and developers. The company's various platforms allow users to share their opinions, ideas, photos and videos, and to engage in other activities. Its products include Facebook, Instagram, Messenger and WhatsApp.

Shares of Facebook were trading marginally lower in Friday trading, down about 0.3% late in the session. The stock has risen nearly 12% so far this year. Over the past year, Facebook shares have gained almost 15%. The company currently has a market cap of roughly $247 billion.