A mile-high mystery is unfolding in Colorado — where family and friends are searching for a man who disappeared without a trace during a Denver Broncos game last week.

Paul Kitterman, 53, and his son, Jarod, 20, were enjoying their first football game at Sports Authority Field on Thursday night after driving from their home in Kremmling with two friends, Denver’s Channel 9 reported.

The father and son, whose seats were not next to pals Tia Bakke and her boyfriend, met up with their buddies at halftime.

“Paul’s like, ‘We’ll see you after the game,’ ” Bakke recalled.

Jarod then went to use the bathroom and was supposed to meet his dad back at their seats. Only Paul never showed up.

“He’s absolutely nowhere to be found,” Bakke said. “It’s been the longest, [most] miserable three days of our lives.”

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Jarod contacted stadium security and police, who scoured Sports Authority Field for the missing dad.

“We were looking everywhere — in parking lots, trees, bushes, anywhere we could think of,” Jarod told local affiliate Fox 31.

Paul, who pals said wasn’t a “technology guy,’’ didn’t have his cellphone with him at the game and was not carrying any credit cards. All he had was about $50 in cash, according to Channel 9.

“Paul is one of the most loyal, responsible people you’ll ever meet in your life,” Bakke said. “He would never, ever just leave you hanging, and especially his son.”

The Kitterman family has filed a missing-persons report, but investigators with the Denver Police Department say they have no reason to suspect foul play, according to Fox 31.

Bakke said Kitterman does not have any medical issues, drug problems or bad blood with anyone.

“This is just so not characteristic of Paul,” she said. “We don’t know what else to do.”