(NewsNation) — Nathaniel Holmes’ parents enrolled in him in an alternative high school in hopes of getting the teen to graduate. But after his mother dropped him off one day, Holmes was never seen again.

Holmes left his school in the middle of the day, borrowed a stranger’s phone to call his mother and then dropped off the radar. That was five years ago.

The 17-year-old from Westminster, Colorado, had just transferred to a new school, with new friends and new influences.

His family told NewsNation they don’t believe Holmes intended to run away, because they were a close-knit family who enjoyed doing things together. Holmes even learned to play the bagpipes to perform alongside his father and his band, Celtic Legacy. A video shows him performing at the Colorado Renaissance Festival.

“It’s one of the proudest moments of my life, playing a tune that I wrote with my son next to me. It was something that I’ll always remember,” Ben Holmes said.

Five months after that performance, Nathaniel Holmes was gone.

“I think he may have fallen in with a bad crowd and I wasn’t vigilant enough to see it,” Ben Holmes said.

He had just transferred to Hidden Lake High School, an alternative program designed to help students graduate.

“He was having a great summer, and then all of a sudden, he goes to this new school, and it just changed him,” said Hannah Holmes, Nathaniel’s sister.

His family said things changed for Holmes, and they suspect he fell in with a group of new friends and began experimenting with drugs.

“His personality went from being really happy to just drained all the time. Tired. He didn’t want to do much,” Hannah said.

On Dec. 19, 2017, Nathaniel Holmes’ mother dropped him off at school. He was late and classes had already started, but Holmes told the principal he needed to speak to a friend.

“Apparently, he wanted to talk with one of his friends, saying he was somewhat nervous about something,” Ben Holmes said.

When the principal told Nathaniel to get to class, he left campus and walked to a nearby park next to the the library, where he borrowed a woman’s phone.

“He called his mother and said, You don’t need to pick me up. I’m going with a friend of my dad’s, which was not true,” Ben Holmes said.

When there was no sign of Nathaniel after school, the family began searching for him. They checked his friends’ houses and drove up and down streets searching for him.

Five years later, they’re still searching and holding vigils. They’re also holding onto a firm belief that Nathaniel is alive, somewhere.

“I do think he’s out there. I do think that he’s going to hear these messages, and if he doesn’t see it, I hope somebody would show him how much my family misses him and wants him home,” Hannah Holmes said.

Age progression photos show how Nathaniel might have aged in the years he’s been missing. Westminster police say they occasionally get tips or reports of possible sightings, but none have panned out.

Ben Holmes said he gets calls too, from scammers trying to prey on the family.

“Just straight-out scammers will call me and say, Well, we know where he is. And if you give us, you know, $3,500, we’ll give you the information,” he said.

For anyone who comes forward with real information, there is a $50,000 reward being offered.

Ben Holmes hopes his message will reach his son.

“I love him and he can come home at any moment, and it would stop my heart from breaking,” Holmes said.

Anyone who has information on Nathaniel Holmes, or thinks they’ve seen him, is asked to call the Westminster Police Department at (303) 658-4360.