HOLLYWOOD - On "Gossip Girl," the deliciously catty prep school drama that debuted on the CW this fall, Upper East Side socialites track each other's misdeeds on an anonymously penned blog that has the power to make or break reputations.

When reformed wild child Serena van der Woodsen was snapped buying a pregnancy test in a recent episode, the photo zoomed through cyberspace and popped up on her classmates' cell phones within moments.

The show's young fans have shown a similar affinity for new media, helping to consistently make "Gossip Girl" the most downloaded television program on iTunes.

But despite the program's online popularity, the network hasn't been able to translate the Web buzz into substantial TV ratings. Even after a marketing push, just 2.6 million viewers on average tuned in to watch the show's first 13 episodes - about 500,000 of them teenagers, its target demographic.

"It's sort of become the first show that has managed to achieve some level of cultural permeation and success in the new world order where ratings don't really seem to apply," said executive producer Josh Schwartz.

For the young network which made "Gossip Girl" the centerpiece of its sophomore season, ratings very much matter.

When viewers watch on new media platforms, "we don't make the kind of money we make when it's on the air," said Dawn Ostroff, the CW's president of entertainment. "That's something still being figured out: How can we take

advantage of viewership shifting to different places?"

That the CW is still trying to boost interest in a program originally regarded as a hot new entrant speaks to the difficulty in gauging how new media are reshaping television viewing. That has caused substantial anxiety in the entertainment industry, which is locked in a bitter labor dispute about how to value the digital space.

"If you believe that all the activity, hype and buzz on the Web translates into viewership, then 'Snakes on a Plane' should have been a blockbuster," said Jeffrey Cole, director of the Annenberg School for Communication's Center for the Digital Future at the University of Southern California, referring to the much-hyped 2006 movie.

"The disconnect seems to be with teens who love to speculate and comment online, but rarely turn it into direct viewing," Cole added.

Indeed, the status of "Gossip Girl" at the bottom of the weekly Nielsen ratings chart belies the show's online activity, executives say.

"When you look at all the ways people are getting 'Gossip Girl' episodes, whether on TV or TiVo or streaming or downloading it, clearly there's a very strong core group of viewers," Ostroff said. "Our job is to start getting the show broadened out a bit."

The success of the "Gossip Girl" relaunch is also pivotal for the CW, formed by the merger of the WB and UPN in 2006. This season marked the first in which the network aired its own programs - not ones developed for the WB and UPN - and executives did not hide their initial excitement about "Gossip Girl."

Based on the bestselling book series by Cecily von Ziegesar, the drama came with a built-in audience and a look inside the world of Manhattan's wealthy youth. The upper-class teens contend with the angst of having too much too soon amid luxurious debutante balls and high-fashion shopping.

When the show drew middling ratings, many in the industry were surprised.

"Gossip Girl" was one of "the shows that we had higher hopes for, that we really believed in," said Andy Donchin, director of national broadcast at the media firm Carat USA. "And we were just disappointed that it didn't do better."

Despite the low ratings, the high concentration of those hard-to-reach viewers has kept it appealing for advertisers; Verizon Wireless and Victoria's Secret have done product integration deals, and the movie "27 Dresses" recently advertised in a content wrap, a multi-part commercial that frames the drama.

The program's feature-laden Web site - which includes postings from Gossip Girl, who narrates the program, and a Second Life portal - was in recent weeks among the top 10 most visited television show Web sites, according to the research firm Hitwise. Visitors to the site initiated 6 million streams of the shows' episodes so far this season.

"Our viewers are early adopters of those technologies, and what you're seeing on 'Gossip Girl' you're going to see more and more on shows that skew older in the future," said executive producer Stephanie Savage.

"There's all this anecdotal evidence that it's much, much bigger than what the ratings would indicate," Schwartz added.

But traditional broadcasters can't afford to forgo TV viewership for online watching, Cole said.

"There's no way to monetize it yet," he said. "The primary value is to engage viewers."