https://techcrunch.com/2018/07/25/facebook-2-5-billion-people/

Facebook today for the first time announced that 2.5 billion use at least one of its apps: Facebook, Instagram, WhatsApp, or Messenger. That’s a helpful number because it counts real people, rather than accounts, since people can have multiple accounts on a single app. That’s compared to 2.23 billion monthly users on Facebook, 1 billion users on Instagram and, 1.5 billion users on WhatsApp, and 1.3 billion users on Messenger.

Mark Zuckerberg announced the new stat on Facebook’s Q2 2018 earnings call following a tough report that saw its user growth slow to its lowest rate ever.