Google, facing growing scrutiny over its approach to consumer privacy, said Thursday it would open its social networking site to teenagers, matching the policies of its rivals, such as Facebook and MySpace.

The move comes as some privacy advocates and lawmakers are seeking special protections for teens online, particularly on social networks where they tend to avidly share information about themselves. It also comes after a controversial move this week by Google to change its privacy policy.

Beginning March 1, the company will follow the activities of users as they move across the firm’s Web sites, including its highly popular YouTube, Gmail and the main search site. The company said the change would apply only to users who are signed into their Google accounts.

Under the new policy, Google said it could track the activities of teens as they surf across the company’s Web sites and pull that information together into a cohesive online portrait.

“With Google+, we want to help teens build meaningful connections online,” Bradley Horowitz, a Google vice president, wrote in a blog post. The decision to lower its minimum age to 13 was triggered by demand from adolescent users, the firm said.

Lawmakers on Thursday began to question the firm’s new privacy policy.

Rep. Cliff Stearns (R-Fla.), Rep. Henry A. Waxman (D-Calif.) and six other lawmakers sent a letter to Google chief executive Larry Page on Thursday, asking whether the new policy will harm consumers. They were particularly interested in why Google account holders, who want to plug into the company’s services, cannot opt out of the new privacy policy.

“We believe that consumers should have the ability to opt-out of data collection when they are not comfortable with a company’s terms of service and that ability to exercise that choice should be simple and straightforward,” the lawmakers wrote.

Separately, Rep. Edward J. Markey (D-Mass.) asked the Federal Trade Commission on Thursday to investigate whether the new policy violates a recent privacy agreement. Google last summer settled a complaint brought by the FTC, which charged that the firm violated consumer privacy by exposing Gmail contact lists to users of the now defunct social network Google Buzz.

Google has 90 million users on Google+ compared with Facebook’s 800 million. In a critique of its rivals, Horowitz wrote in a blog post that rival networks don’t adequately shield users from oversharing, which privacy advocates say can ruin reputations and expose youths to predators and bullying online.

He said teens on Google+ can create customized circles of contacts to share information such as pictures, links and other content only to specific friends. Those circles of contacts make it harder for information to leak to the public, he said.

And before a teen decides to share something publicly, the sites encourages the user to pause and think harder about the decision to post.

“Sadly, today’s most popular online tools are rigid and brittle by comparison, so teens end up oversharing with all of their so-called friends,” Horowitz said.

Facebook sets 13 as its minimum age and enables users to prevent personal information from becoming public. Consumer Reports has reported than an estimated 7 million U.S. users on Facebook are younger than 13 and in violation of the user agreement.

Some privacy advocates commended Google for safety features directed at teens and has been clear in explaining to users how to safely set up privacy controls. But they expressed concerns that youths may not grasp Google’s new privacy policy.

“Google has been clear about how it will work, but how good is a 13-, 14-, or 15-year-old at understanding it?” said Alan Simpson, vice president of Common Sense Media, an advocacy group for the safety of children online.