Causes are ticked off easily. Mentioned often is the high teenage unemployment rate, reaching 20.2 percent among 16- to 19-year-olds, far above the national rate of 6.7 percent.

Cheap fashion has also driven a more competitive market. So-called fast-fashion companies, like Forever 21 and H&M, which sell trendy clothes at low prices, have muscled into the space, while some department stores and discount retailers like T. J. Maxx now cater to teenagers, as well.

“You can buy a plaid shirt at Abercrombie that’s like $70,” said Daniela Donayre, 17, standing in a Topshop in Manhattan. “Or I can go to Forever 21 and buy the same shirt for $20.”

Online shopping, which has been roiling the industry for years, may play an especially pronounced role in the teenage sector, analysts say. A study of a group of teenagers released in the fall by Piper Jaffray found that more than three-fourths of young men and women said they shopped online.

Not only did teenagers grow up on the Internet, but it has shaped and accelerated fashion cycles. Things take off quickly and fade even faster, watched by teenagers who are especially sensitive to the slightest shift in the winds of a trend.

Matthew McClintock, an analyst at Barclays, pointed to Justin Bieber as an example.

“Today, if you saw that Justin Bieber got arrested drag-racing,” Mr. McClintock said, “and you saw in the picture that he had on a cool red shirt, then you can go online and find that cool red shirt and have it delivered to you in two days from some boutique in Los Angeles.