SAN FRANCISCO — If you post something on Facebook, let there be no doubt that it can end up as an ad shown to your friends and acquaintances.

Facebook pressed forward on Friday with official changes to its privacy policies, first proposed in August, that make the terms of using Facebook more clear than ever: By having an account on the service, its 1.2 billion global users are allowing the company to use their postings and other personal data for advertising.

And teenagers are no exception. Although the company deleted language that said parents were implicitly consenting to ads featuring their children’s posts by letting them use Facebook, the company said it was already getting that permission when teenagers sign up to use the service.

After the proposed changes were originally announced, they drew an outcry from many users, some privacy groups and members of Congress, and prompted the Federal Trade Commission to scrutinize the company’s plans.