MENLO PARK, Calif. — Mark Zuckerberg declared in March that he planned to shift Facebook away from being a public town square and to private communications. Now, the chief executive is rolling out the first in a series of changes to achieve that.

On Tuesday at its annual developer conference, Facebook unveiled a redesign of its mobile app and desktop site. The revisions add new features to promote group-based communications instead of News Feed, where people publicly post a cascade of messages and status updates.

With the changes, users can more easily message one another and share news and other items with members of private groups on the site, the company said. Mr. Zuckerberg is working to integrate and encrypt Facebook’s different messaging services, which include WhatsApp and Messenger. The company also plans to continue emphasizing its Stories product, which allows people to post updates that disappear after 24 hours. And it unveiled a spare, stark white look for Facebook, a departure from the site’s largely blue-tinted design.

The features, when combined, “will end up creating a more trustworthy platform,” Mr. Zuckerberg said in an interview. “Everywhere you can see and connect with friends, you’ll be able to see and connect with groups; it’s going to be woven into the fabric of Facebook.”