“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.