You might think that it would be worried, overprotective mothers who would rebel against the overt sexualization of the teenage star Miley Cyrus, who became a pop phenomenon as Hannah Montana on the Disney Channel hit show. But no. It’s the young girls who think Ms. Cyrus has gone too far. And many of them are moving on.

Perry Hamm, who lives in the San Francisco Bay area, has adored Hannah Montana since the age of 8. At 10 she bought a ticket to “Hannah Montana: the Movie,” along with one of the three million soundtracks sold after the film’s debut. Last September she scored one of the most coveted tickets among teenagers in 2009: Hannah Montana in concert.

But now at 11, Perry’s enthusiasm for the 17-year-old Ms. Cyrus has fizzled. She wishes Ms. Cyrus would ditch the tight T-shirts and Uggs for the sassy skirts her television persona wears. And she is still puzzled why Ms. Cyrus posed seemingly nude, a sheet draped around her chest, in Vanity Fair two years ago. “I don’t know what was going on in her head,” Perry wondered aloud.

So last month, when Ms. Cyrus released her post-adolescent anthem, “Can’t Be Tamed,” her once-adoring fan was unimpressed, unmoved by, among other things, the singer’s sexy music video.

“It was weird,” Perry said of Ms. Cyrus’s bird wings and black ribbon corset. “I feel like she acts 25. She looks so old. She is too old for herself.” She, like others her age, has had enough. First-week album sales for the more adult “Can’t Be Tamed” tallied a mere 102,389, according to Nielsen SoundScan, which tracks music sales. That was 72 percent less than her 2008 solo debut, “Breakout,” and 33 percent less than last year’s “Time of Our Lives,” both of which were popular with teenagers.

Ms. Cyrus’s appeal among those age 13 to 17 has dropped, too, according to E-Poll Market Research, a brand and celebrity research firm. Of those surveyed online recently, only 24 percent said they liked or liked her a lot, compared with 45 percent in 2008. Those who track preteens are noticing the shift. Tina Wells, a market research executive who consults with Fortune 500 companies, said Ms. Cyrus ranked No. 7 in April on its list of celebrities considered cool by children 8 to 12 years old. Two years ago she was No. 1.

Ms. Cyrus declined to be interviewed because she is preparing for her next movie role, said her spokeswoman, Meghan Prophet. But, according to posts on her blog, Ms. Cyrus is ready for a fresh start. “I’m super excited for this new chapter of my life to begin,” she wrote on June 11.

It is tricky for any teenage star to navigate the path to adulthood. (Britney Spears? Lindsay Lohan?) But Ms. Cyrus, it seems, is alienating her fans faster than she is gaining new ones. Partly to blame is last year’s pole dance at the Teen Choice Awards, and the recent video posted on TMZ of her giving a lap dance to a 44-year-old film director.

For some mothers of Ms. Cyrus’s fans, her wrenching transition from teen idol to sexual icon has become a teachable moment.

“I’m just impressed with kids picking up on the change and saying it’s not that interesting and they don’t relate,” said Megan Calhoun of Ross, Calif., the founder of TwitterMoms, a blog for mothers that has 26,000 members. Some have expressed dismay at the shift in Ms. Cyrus’s persona. “It’s almost as if these young stars don’t realize it is a turnoff,” Ms. Calhoun said.

Some parents chalk up her behavior to teenage angst. “It doesn’t surprise me what she is going through,” said Wendy Ellis, a mother of two from Odenton, Md. “The raging hormones. She is testing the limits of the box and what is appropriate.”

But young girls are not always as forgiving as their mothers. Jenna Ellis, 7, said she watches “Hannah Montana” only when her 9-year-old sister, Regan, isn’t watching Nickelodeon’s “iCarly,” a popular series about a young girl who creates her own Web show. Jenna doesn’t want Ms. Cyrus to “do what she doesn’t want to do,” but added, “I wish she’d be the same as the show.”

Indeed, much of the conversation about Ms. Cyrus between Ms. Ellis and her daughters has focused on the notion that Miley Cyrus and her television alter ego are separate personas. Regan, for one, said she is bored by Ms. Cyrus’s new act. “She used to be more kid-friendly, sweeter,” Regan said. “Now she is just Miley.”

Ms. Ellis said she discussed with her daughters whether it was appropriate for them to wear clothes like Ms. Cyrus’s. Regan reasoned that Ms. Cyrus wore tiny shorts because she was hot on the set. “It’s not my job to tell Miley Cyrus how to dress,” her mother said. “If I’m uncomfortable I will turn it off.”

Parents can’t monitor what their children view every minute. Valerie Gonzalez, 15, of San Fernando, Calif., has enjoyed Hannah Montana’s wholesome antics since the show’s 2006 debut. That is why she was shocked when she turned on the “Teen Choice Awards” last August and saw Ms. Cyrus dancing in top-of-the-thigh shorts and black boots.

“What I don’t like so much is she is exposing herself,” Valerie said. Recently, she was struck by Ms. Cyrus’s writhing on a bed of peacock feathers in the “Can’t Be Tamed” music video. “I don’t think she is going down the right path,” Valerie said.

Teenagers are Ms. Cyrus’s core demographic, but the singer is seeking older fans, too, which puts the onus on parents to explain her motives. One member of TwitterMoms posted a comment about her daughter, saying, “It’s my job as a parent to explain to her why Miley is changing and to point out she is a performer, an actress and singer.”

Gary Marsh, president of entertainment and chief creative officer of Disney Channels Worldwide, said that teenagers seem to be differentiating between Ms. Cyrus and the character she plays. That is good for Disney, which has one last season of episodes and a warehouse full of “Hannah Montana” products to promote. (Disney has sold 13.2 million “Hannah Montana” albums and the show is the No. 1 cable show among 9- to 14-year-olds. It is seen in 150 countries.)

Mr. Marsh said it is not Disney’s responsibility to guide her through the transition. “The network’s role is not to give personal advice,” he said.

Besides, there is always a fresh face to satisfy the teenage crowd. Valerie Gonzalez is now smitten with Selena Gomez, who stars in Disney’s “Wizards of Waverly Place.” And few can ignore the demure 20-year-old female country singer who has become a favorite: Taylor Swift. Already Ms. Ellis has had to explain to Regan what the phrase “gave everything she had to a boy” meant in Ms. Swift’s song “15.”

Still, Perry Hamm could barely contain her excitement when she brought up her name.

“I think she is so adorable,” she squealed. “I think her songs are really catchy!”