Shares of Urban Outfitters aren’t cool anymore.

That was the word among investors yesterday, who sent the hipster clothier’s stock plunging 19 percent after the shocking announcement that star CEO Glen Senk is leaving after 17 years with the company.

Retail insiders were equally flummoxed by the news that 55-year-old Senk was skipping out of Urban — a $2.4 billion retailer with one of the industry’s best track records of the past decade — to join David Yurman, a sleepy, privately-held New York fashion jeweler.

While Senk couldn’t be reached for comment yesterday, one source close to the situation insisted, “There’s no smoking gun here, no hidden problems.”

Senk, who already sits on the board of David Yurman, “sees the opportunity to make it into another Coach or Tiffany,” the source said.

Whatever the potential for David Yurman, analysts fretted that the prospects for Urban Outfitters look dimmer without its longtime merchant prince.

“We believe bulls were focused on management quality, particularly at the CEO level, as retail stories are very dependent on management team talent,” said Jefferies analyst Randal Konik. “This latest news puts the company’s strategic direction in question and puts a hole in the key bull thesis.”

Urban Outfitters shares yesterday — which had steadily rallied in the fall on hopes that a turnaround was gaining traction after more than a year of disappointing performance — tumbled $5.48 to close at $23.93.

Meanwhile, the retailer is facing increased competition from fast-growing, lower-priced chains including H&M, Forever 21 and Uniqlo.

“The timing is quite tough,” said Barclays Capital analyst Stacy Pak.