SALT LAKE CITY (ABC4) – Frank Frost was six-years-old when his sister disappeared.

It was July 1984 and the family lived in Salt Lake City. The younger Frost recalled the adults in the home talking about Debbie Frost but he was not involved.

“She had runaway a couple of times before,” Frost said. “But she had always been in contact with her dad and her aunt.”

A day after she vanished a missing person’s report was filed with Salt Lake City police.

The report said Debbie Frost was “last seen by her boyfriend.” He also said she was “missing” for about 24 hours” and that she’d “ran away before.”

Soon the public learned of her disappearance. According to one media report, Frost “never arrived home” that night. Police considered “foul play” and she was not considered a runaway because “she’s happy and planning a birthday party for her boyfriend.”

“I was aware something happened,” said Frank Frost. “(I understood) that Debbie was gone and they were looking for her.”

Four years passed and Frost had not been found. Her brother was now ten-years-old.

“I started bugging the homicide unit of the Salt Lake police department,” he said. “Yeah as a 10-year-old. This is pretty heavy stuff for a ten-year-old to be dealing with. But I wanted to find out what happened to my sister.”

He claimed police considered her as a runaway and that she would eventully return. He left disenchanted.

The young Frost wouldn’t give up. He sent letters to Unsolved Mysteries, America’s Most Wanted and to the media.

“I had spent all of the money I had earned, my allowance money, putting together these packets, going to Kinko’s and copying everything and mailing them out,” he said.

The 10-year old never heard back from anyone. Debbie Frost was forgotten in the public’s eye.

But he continued his writing campaign throughout his teen years.

“I felt there was a hole in my heart that should have been filled by my sister,” Frost said. “The memories I do have of her are nothing but love and I just wanted to know what happened.”

It wasn’t until 2011 that he finally learned of a new development. Someone had befriended her back in 1984.

“I don’t think they’ll ever find her,” said a former friend who knew both. “It’s sad. She’s a good person. She didn’t deserve what happened to her. ”

Missing In Utah will continue its story of the disappearance of Debbie Frost on Thursday.