"The Messenger team's mission is to make Messenger the best place to communicate with all the people and businesses in the world," Facebook head of messaging products Dave Marcus said in an online post.
"I'm happy to report that we've made a good step in that direction, and toward the end of 2015, we crossed the milestone of 800 million people using Messenger every month."
He maintained that while the number was impressive, it was still "early days" for Messenger.
Facebook also began testing on weaving its "M" digital virtual assistant into Messenger. The test of enhancing Messenger with artificial intelligence is "going well," according to Marcus.
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Facebook last month announced an alliance with Uber that lets people in the United States summon cars from the ride-sharing service using the Messenger application.
The partnership was a major move for both California firms, further expanding Facebook's stand-alone messaging service beyond simply communicating and putting Uber in touch with a huge user base.
"You can expect us to keep trying new things, too," Marcus said.
"There will be more innovative developments to come from Messenger this year."
Plans for this year include doing more to enable businesses and services to connect with people using Messenger, according to Facebook.
Messenger is working with players in e-commerce, travel, aviation and other industries to test modes of interacting with people on the service, Marcus told AFP in an interview here.