A social media milestone is reached.

FOX's Chris Foster reports: 

Facebook announces it now has two billion monthly active users, accounts logged into in the last 30 days. Some people may use more than one account, but still, it's more than a quarter of the world's population.

The company's chief executive Mark Zuckerberg writes in a Facebook post, "it's an honor to be on this journey with you."

Facebook reached one billion users five years ago. It's by far the most popular social media network. The Chinese service 'We Chat' is second, with more than 900 million monthly active users.

Twitter reports more than 300 million.

Chris Foster, FOX News.