WhatsApp, the stand-alone messaging app owned by Facebook (META -0.47%), has become the second social networking platform to serve 2 billion different users in a single month according to a blog post at the WhatsApp website. The first to reach that mark, of course, was Facebook itself back in June of 2017. It's continued to grow its user base, reporting 2.5 billion people were visiting its social media platform as of the end of last year.

Photograph of many people coming together in the shape of an arrow.

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Facebook itself allows members to send direct messages to other members, but within the confines of the app or website. WhatsApp is only a messaging app (though offers a PC-based option) built from the ground up with privacy and security technologies in mind. The unattributed blog post noted, "We know that the more we connect, the more we have to protect. As we conduct more of our lives online, protecting our conversations is more important than ever. That is why every private message sent using WhatsApp is secured with end-to-end encryption by default."

YouTube is just as big, but different

Although Facebook and now WhatsApp rate as the world's busiest platforms in terms of return users and Facebook is among the world's most visited sites, neither are exactly alone when it comes to drawing a large crowd of different users month in and month out. Alphabet (GOOGL -4.44%) (GOOG -4.50%) property YouTube also reported early last year it was sharing videos with 2 billion unique visitors every month.

The advertising models are different for each service though, reflecting the clear differences with each of their respective apps or websites. Specifically, WhatsApp doesn't create public-facing web pages, and YouTube isn't a social networking website.