A California teen with a history of mental health struggles vanished during a layover in Colorado late last month.

Harper Cadman, 15, was last seen at Denver International Airport around 8:30 a.m. on Jan. 30, her mother, Ari Petronelli, wrote on Facebook.

Cadman — who was in the process of being transferred from treatment in Montana back to California — never made her connecting United Airlines flight, her desperate mother explained.

Her checked luggage made it to Los Angeles, but Cadman has not been heard from for nearly two weeks.

Authorities believe the teen may now be in the Denver or Boulder areas.

“My sister and I spent last week searching Denver and Boulder, speaking with detectives, advocates, the unhoused, and ‘street kids,’” Petronelli wrote.

“What we saw was a very cold, scary, and dangerous situation for anyone but especially an at-risk 15-year-old girl who was last seen wearing just a sweater with leggings and no belongings,” she lamented.

“Harper does not know anyone in Colorado and has only been when she was 8 years old for a vacation so she is not familiar with the area,” Patronelli said, adding that Cadman has gone missing before.

The teen is 5 feet, 7, inches tall and 115 pounds, according to the National Center for Missing and Exploited Children.

She has blue eyes and dyed black hair, facial piercings, and tattoos on her waist and middle finger of her left hand. She also has braces.

It is unclear why Cadman was traveling without an escort.

Patronelli and the Denver Police Department did not immediately respond to The Post’s request for comment.