Lonelygirl15 appears to be an innocent, home-schooled 16-year-old, pouring her heart out for her video camera in the privacy of her bedroom. But since May, her brief posts on the video-sharing site YouTube and the social networking hub MySpace have launched a Web mystery eagerly followed by her million-plus viewers: Who is this sheltered ingenue who calls herself "Bree," and is she in some sort of danger -- or, worse, the tool of some giant marketing machine?

No one has publicly come forward to lay claim to her work, but she is starting to look as connected in Hollywood as any starlet. Three lonelygirl15-obsessed amateur Web sleuths set up a sting using tracking software that appears to show that e-mails sent from a lonelygirl15 account came from inside the offices of the Beverly Hills-based talent agency Creative Artists Agency.

The apparent CAA link takes its place alongside other tantalizing pieces of evidence that lonelygirl15 is not who she claims to be: a copyright for the name obtained by an Encino lawyer, and a plot line that, leading speculation suggests, will turn out to be the lead-in to a horror movie's marketing campaign.

CAA spokesman Michael Mand said he "could neither confirm nor deny" that the agency is representing whoever is behind the 27 video posts. (Other talent agencies and production companies contacted by The Times denied any connection.)

As to horror film rumors, calls made to several studios found no such plans -- but plenty of fascination for the way in which a Hollywood-ready cultural phenomenon has been built from a grass-roots Web platform. Lonelygirl15, many say, is the next-generation "Blair Witch Project," using interactive forms of storytelling that, like the 1999 hit, tries to trick an audience into thinking it's true.

Indeed, if a commercial project does result, lonelygirl15 may prove to be a model of how to harness a groundswell created on seemingly populist, user-driven websites such as YouTube and MySpace.

To fans, meanwhile, it doesn't seem to matter whether lonelygirl15 turns out to be a private citizen or part of something bigger.

Riana Giammarco, a Rhode Island 20-year-old who curates a lonelygirl15 discussion board (one of several on the Web) says the mystery is the principal draw for her.

"I like the community aspect of the mystery -- getting together and trying to figure it out," Giammarco said in a phone interview. "Though I would still watch if there weren't a mystery, the videos wouldn't appeal to me as much."

Lonelygirl15 began quietly, posting in May two amateurish tributes to other videos on the Web's confessional arenas. For a moment she was just one of thousands who post videos on the site each day, typically young people speaking into cameras about their personal lives, a familiar trope from reality TV.

On June 16, lonelygirl15 made her first appearance in a video, titled "First Blog/Dorkiness Prevails." Dark-haired, big-eyed and pretty, she blinked nervously and hugged her knees as she described living in a small town "hours from a mall" with strict religious parents and a friend named Daniel, who she didn't like "in that way."

Over the next three months, two dozen more videos hit the Web, spaced out every few days. Bree dangled hints about her life, revealing that she had spent her youth in New Zealand, was treated for "lazy eye" and had an obsession with physicist Richard Feynman. Oblique references popped up to "my religion," which was never named but which forbade things such as attending Daniel's high school graduation party.

Fans soon started to notice jarring details. A music clip from an undiscovered L.A. band was mixed in to her well-edited montage sequences. Her room was movie-set neat. Above her bookshelf hung a photo of famed occultist Aleister Crowley. Thin already, Bree talked about an upcoming religious ceremony that she would participate in, even though it involved going on a diet.

On the message boards, discussions revolved around the single shoot theory: that the videos must have been filmed in one batch, because they gave little or no nod to the furor erupting around them. The landscape of two outdoor videos had botanical clues that suggested Southern California.

Since June, the videos have regularly made it to the top of YouTube's daily "Most Viewed" list, averaging about 200,000 views each, with several topping 600,000 -- viewership many cable TV executives would kill for.

In late August, fans discovered that the Web address for lonelygirl15.com had been purchased before the first video even appeared, with efforts made to shield the identity of the buyer.

In early September, Web forums erupted with the news that lonelygirl15 had been trademarked and the application filed by an Encino lawyer named Kenneth Goodfried. (He declined to comment for this article.) Within days, the MySpace profile of Goodfried's daughter was being combed for connections to the video.

Independent film director and blogger Brian Flemming, who is known for creating edgy film events, became wrapped into the story when viewers became convinced that Flemming had constructed the whole thing in order to promote an upcoming film.

Flemming said he received more than 300 e-mails from people accusing him of involvement.