By Sara Vilkomerson

August 12, 2008 | 8:08 p.m

The young woman who approached the table by the window at the Pinkberry on Eighth Avenue and 18th street was nervous, breathless. She was sorry to interrupt, sorry to be a bother, she said. It was just that she loved Taylor Momsen so much.

The just-barely-15-year-old Ms. Momsen, who plays aspiring queen bee Jenny Humphrey on the CW show Gossip Girl, gave the woman—who looked to be at least in her mid-20s, and was clutching a napkin and shaking like a whippet in winter—a warm, practiced smile and helped her locate a pen and piece of paper so she could sign the autograph on something suitable. Ms. Momsen scribbled her name with a girlish curlicue flourish, and offered a friendly wave goodbye as her fan skipped elatedly out the door.

It’s a regular occurrence now for Ms. Momsen (“The older girls get nervous. The younger girls, cry,” she said), who, over the summer, has become the obsession of a strange and ragged slice of New York. Even as her co-stars have ascended the ladder of gossip-worthiness—the golden-locked goddess Blake Lively and the impressively sideburned Penn Badgley have had a very public romance while dandy-dressing, secretly English Ed Westwick has hardly been shy about his carousing—Ms. Momsen has emerged as the show’s true It Girl: admired, lusted after and, of course, scorned. Girls and young women covet her style (which ranges from bright, simple and sophisticated to mix-and-match punk). Boys and men—in their teens and 20s and beyond—can’t help but be drawn to her coltish beauty (even as that fact could make them uncomfortable). And there are the requisite haters, too, so unnerved by Ms. Momsen’s uncanny poise and sudden ubiquity that they can’t help but snipe at her. As photographs of her—on location for Gossip Girl, making the rounds at parties and movie premieres, riding the subway around her newly adopted city—have cropped up on celeb-tracking blogs and Web sites, they’ve also collected captions and comments snarky and vicious enough to be straight from the cell phone of Gossip Girl’s eponymous blogger.

“Our thanks to Taylor Momsen and Ali Lohan for making 14 the new 35,” wrote a commenter on Gawker, under a photo of the actress in a froofry yellow frock at the Fifi fragrance awards in May. Captions for other snaps have included “Little Bitch Stops for Itch” (this was later changed) and “Taylor Momsen Forgot her Pants.”

But is it Taylor we love to love, and love to hate? Or Jenny, who practically ran away with the show last season as she plotted her path to the top of the prep school food chain? Ms. Momsen understands how people might get confused.

“It’s funny because I forget that I look the same—you know, that I look the same all the time,” said Ms. Momsen, as she spooned original-flavored Pinkberry yogurt covered in Fruity Pebbles into her mouth. “I have two different modes: I have my on-set mode, and then I have my mode with my friends and family. My Taylor mode. And when I’m in my Taylor mode, I forget that people still see me as Jenny. It takes a minute.”

If we can’t remember, it may be because we don’t want to. She may be a teenage social-climbing bitch, but Jenny Humphrey has lifted Gossip Girl from sudsy teen drama to genuinely gripping television, and brought us the most lovable villain we’ve seen in ages.

The New Eve Harrington

A day before our Pinkberry date, at the Silvercup Studios set of her show, Ms. Momsen was working through a scene that would be familiar to any regular Gossip Girl viewer. It was breakfast time at the Humphrey loft, and artificial sunshine streamed through the fake windows, drenching the very-hard-to-believe-this-family-is-supposed-to-be-poor loft with light, while the Humphreys themselves bantered wittily around a kitchen counter. For those who haven’t fallen pray to the show’s charm, a primer: Gossip Girl peeks into the rarified air and lives of the Upper East Side’s privately schooled elite. Based on the best-selling series by Cecily von Ziegesar, and developed by O.C. masterminds Josh Schwartz and Stephanie Savage, the show is a delicious weekly Greek tragedy, filled with scandalous sex, betrayals, drinking, drugs, homosexuality, embezzlement, sinister plotting and social hierarchy coup d’état, all recorded on the anonymous Gossip Girl blog. Each gleaming setting—the shiny town cars, the opulent limestone townhouses, the bejeweled department stores—and reference to exclusive New York City hot spots screams privilege and invites a peek into that ever-lusted-after moneyed unknown (Ms. Savage has previously said that the Sofia Coppola film Marie Antoinette helped inspire the look of the show).

Jenny’s family isn’t a natural part of the socialite spectrum (they live not in the East 80s but in—gasp!—Brooklyn), and she and her older brother Dan (Mr. Badgley) are the perpetual outsiders. When we met them in the first season, Dan was a brooding aspiring writer (dubbed Lonely Boy by Gossip Girl) who found himself thrust into the inner circle by dating über-chic Serena Van der Woodsen (Ms. Lively), while Jenny was a wide-eyed naif, awed and intimidated by the rich and glamorous popular girls. Dan kept his head straight for the most part, but Little J couldn’t help but make a power play for the top, initiating a tug of war with Blair Waldorf (Leighton Meester), who may be the scariest raven-haired actress we’ve seen since Shannen Doherty stormed off 90210.