Mr. Zuckerberg also spoke about his company’s ambitions to host TV-style live video, an initiative that some media companies, including The New York Times, are investing in seriously, despite uncertainty about the rates at which videos will be monetized.

Facebook also announced that it would open up Instant Articles — which encourage publishers to post their content directly to Facebook — to “any publisher.” The company demonstrated chat bots, through which users can interact directly with media companies, including publishers, through Facebook’s Messenger app.

“Messenger is going to be the next big platform for sharing privately, and for helping you connect with services in all kinds of new ways,” Mr. Zuckerberg said, after demonstrating a CNN chat bot on stage.

At the same time, publishers pored over a report from the analytics firm Parse.ly, detailing how important Facebook had become to their business: Among sites tracked by the firm, more than 40 percent of web traffic came from the social network.

Facebook’s users seem to be following Mr. Zuckerberg’s lead. NewsWhip, which tracks how publishers are performing across major Internet platforms, says the rate at which links to outside websites are shared on Facebook, compared with videos and Instant Articles, has declined.

Liam Corcoran, NewsWhip’s communications director, says that in recent months a wide range of publishers have called him to ask whether sudden drops in Facebook reach are widespread, and asking how they might be remedied — as if they were asking how to cure a disease.

“It’s a doctor’s office,” he said.

So far, publishers are responding in a variety of ways. With the help of venture capital funding, companies like BuzzFeed and Vox are investing heavily in video production with a focus on TV and film. Others, like Mashable, are diverting resources to increasing their audience on Facebook, hoping that enough money — through revenue-sharing arrangements with the company — will follow.