Brendan Erazo, 15, of Daytona Beach, Fla., mixes and publishes his own Christian-themed dance tracks under the name DJ Xsjado at the Kids' Internet Radio Project.

Melissa Paredes, a 16-year-old in Lompoc, Calif., maintains a Web site where she writes poetry, posts pictures and shares music. So when she was mourning her stepfather, David Grabowski, earlier this year, she reflexively channeled her grief into a multimedia tribute.

Using images she collected and scanned from photo albums, she created an online slide show, taking visitors on a virtual tour of Gabrowski's life -- as a toddler, as a young man, at work.

"It helped me a lot," Paredes said in an instant message, the standard method of communication among the millions of American teenagers who, according to a study by the Pew Internet and American Life Project, are fast becoming some of the most nimble and prolific creators of digital content online.

For all of its poignant catharsis, Paredes' digital eulogy is also a story of the modern teenager. Using the cheap digital tools that help chronicle the comings and goings of everyday life -- cell phone cameras, iPods, laptops and Web editing software -- teenagers like Paredes are pushing content onto the Internet as naturally as they view it.

"At the market level, this means old business models are in upheaval," said Lee Rainie, the director of the Pew project. "At the legal level, this means the definition of property is up for grabs. And at the social level, it means that millions of those inspired to create have a big new platform with which they shape our culture."

According to the Pew survey, 57 percent of people 12-17 who are active online -- about 12 million -- create digital content, from building Web pages to sharing original artwork, photos and stories to remixing content found on the Web. Some 20 percent publish their own Web logs, or blogs.

That reality is inextricable from the broader social, cultural and, sometimes, as in Paredes' case, deeply personal experience of being a teenager. And it is one that will undoubtedly have profound implications for the traditional managers of content, from big media companies and libraries to record labels, publishers and Hollywood.

From school libraries and living rooms, millions of teenagers are staking out cyberterritory in places like MySpace.com, Xanga.com and Livejournal.com, where they matter-of-factly construct their individual online presence.

It's that kind of enthusiastic self-revelation that has begun prompting parents and school districts to begin monitoring -- and in some case banning -- sites where teenagers have taken up residence.

Last week, Pope John XXIII Regional High School in Sparta, N.J., banned students from posting on MySpace.com or similar sites, citing concerns that students were unwittingly revealing too much information about themselves to potential cyberpredators.

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