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Facebook has reached a new milestone: 1 billion people using the social network in a single day.

Facebook reached the high mark on Monday, CEO Mark Zuckerberg wrote in a Facebook post on Thursday. That means roughly "1 in 7 people on Earth used Facebook to connect with their friends and family" in a single day, he added.

Facebook is by far the world's largest social network with 1.5 billion monthly active users. Twitter, by comparison, has 316 million monthly active users. The social network has seen steady growth, with mobile users becoming a key part of its success. More than 87 percent of the 968 million people who log into the social network each day do so from a smartphone or tablet, according to Facebook.

For Facebook, mobile growth means big bucks. In July, the social network said 76 percent of advertising revenue came from mobile devices for its second quarter. While Facebook doesn't say how much money it makes from advertising overall, it is expected to make up a vast majority of its sales. Last year, Facebook accounted for more than 18 percent of global advertising spent on mobile devices, according to industry researcher eMarketer.

"Our community stands for giving every person a voice, for promoting understanding and for including everyone in the opportunities of our modern world," Zuckerberg wrote. "A more open and connected world is a better world."

Facebook's mission to connect the world now expands far beyond its namesake social network. Some 700 million people have used the company's Messenger mobile messaging app, Facebook said in July, and Instagram, the Facebook-owned photo and video sharing app, boasts 300 million monthly active users.

Another milestone may be in the offing for Facebook as the company undertakes initiatives to spread Internet -- and its social network -- around the world. The company's Internet.org initiative, which provides free Internet access via a mobile app and website, is available in parts of Africa, Latin America and Asia. And Facebook is testing a solar-powered drone that could beam the Web down to Earth in places where Internet access is limited.