A 16-year-old girl who attends Horace Mann is posing with a cigarette dangling from her lips. She says she likes Champagne and Marlboro Reds. A student at Hewitt, also 16, is posing in a sateen pink bodice. She says she likes sipping Midori martinis and lists her occupation as “muse.”

They are just two of the thousands of local teenagers who are posting photos, listing information about themselves, and potentially chatting with people they have never met on the popular social networking site, Myspace.com.

Just more than 2 years old, the free, ad-supported site has attracted more than 50 million users, with about 150,000 signing up each day; about a quarter of them are minors.

A spate of highly publicized assaults against girls who allegedly met their attackers on Myspace has caused some of the city’s private schools and parents to take notice.

Last week, Packer Collegiate in Brooklyn Heights sent home letters instructing parents how to log on and find out if their sons and daughters have published profiles.

According to an article in the Packer Prism, more than 150 students have profiles that they visit almost every day. Many belong to groups, including one called, “Hi my name is ___ and I go to a N.Y.C. private school.”

“They are posting things that are private but they are doing it in a public domain,” Packer Collegiate’s assistant head of school, Matthew Nespole, said. The school is hosting a community forum at the end of the month to educate parents about the site.

Myspace, which invites subscribers 14 and over, follows the lead of sites such as Friendster and LiveJournal, but its soaring popularity has made it the focus of attention of schools, parents, and police across the country.

A Catholic school in Florida suspended about a dozen students earlier this month for posting “inappropriate” language on their Myspace profiles. Seven high school basketball players in Lincoln, Neb., were suspended from their teams after school officials found photos of them drinking what appeared to be alcohol in photos posted on Myspace.

At Brearley, the rigorous all-girls school on the Upper East Side, a technology expert is delivering a lecture, “They’ve got mail: You’ve got trouble: a look at raising kids in a digital world.” Ramaz, a Jewish day school, sent parents a letter about a month ago informing them about Myspace after administrators discovered that students were posting there.

Many parents have been alarmed to discover that their children were lying about their ages and publishing sexually suggestive photos.

The Horace Mann School in the Bronx has hosted four forums over the past three weeks to inform parents and faculty about the site.

“It’s where kids are spending their time,” the director of technology at Horace Mann, Adam Kenner, said. “They’re taking time to create a version of themselves online with photos and I don’t think that this is the version they really want to present.”

Mr. Kenner warns that while students may think they are just using the site to communicate with friends, college admissions officers and employers also peruse Myspace looking to find out what they can about applicants.

Myspace was created in 2003 as a social network for bands and aspiring musicians. Rupert Murdoch’s News Corporation purchased the site for $580 million last July. It is now the third most trafficked site on the Internet, according to Parry Aftab, who runs the Internet safety group WiredSafety.

“Now it’s Fox and the Post and it’s a huge commercial enterprise,” Mr. Kenner said. “Talk about a haven for market research: You have 57 million teenagers giving you their buying habits, shopping habits, and their likes and dislikes,” he said. A spokesman for Myspace did not return a call seeking comment.

Horace Mann has encouraged students to think carefully about the information they post and what happens when they remove it. “Is the information really gone or does Rupert Murdoch still have it?” Mr. Kenner asked.

Still, some students say parents are overreacting and that they mostly use the site to talk with friends. They said users don’t have to respond to e-mails from strangers. A group of 11th-graders at Horace Mann said Myspace is already sort of “yesterday” and that they have moved on to other sites such as Facebook.

Sidwell Friends School in Washington, D.C., recently prohibited students from using their school e-mail addresses to register on Facebook. Access is limited to users with high school or college e-mail addresses. So far, the New York City Department of Education has not placed a citywide ban on access to sites like Myspace and Facebook at high schools, but principals are free to block Web pages of their choosing.