"As of this morning, the Facebook community is now officially 2 billion people!" Zuckerberg wrote in a post marking the milestone.
"We're making progress connecting the world, and now let's bring the world closer together," he wrote. "It's an honor to be on this journey with you."
Facebook's announcement came as it works to redefine its purpose, led by Zuckerberg who traveled the US this year to better understand what people want out of the social network.
"We realize that we need to do more too," the 33-year-old said in a recent interview with CNN Tech.
"It's important to give people a voice, to get a diversity of opinions out there, but on top of that, you also need to do this work of building common ground so that way we can all move forward together."
The firm's new mission statement says it seeks "to give people the power to build community."
Zuckerberg's message was echoed by Naomi Gleit, a vice president at the internet giant, who credited the millions of small communities emerging within Facebook for helping drive growth.
More than a billion people take part each month in Facebook "groups" -- built around everything from sporting interests to humanitarian projects, she said in an online post on Tuesday.
For Gartner analyst Brian Blau, Facebook appears to be striving to become "more of a community company than a technology company."
He noted that Facebook's role in last year's contentious US election -- during which social networks were awash in misinformation -- may have been a motivating factor.
