LAKEWOOD, Colo. -- The U.S. Marshals Service has joined the search for a missing 16-year-old Lakewood girl who ran away last week with a convicted sex offender.

Police believe that Amber Nicole Westbrook was involved in an ongoing relationship with Matthew Preston Caulk, a convicted sex offender more than twice her age. Police said Amber met the 40-year-old Caulk at the apartment complex where she lived and where Caulk was living and working odd jobs.

"He uses his personal charm to ingratiate himself with minors, and is able to gain their confidence and perpetrate his crimes," said Deputy U.S. Marshal David Floyd.

Authorities worry that Amber may be in danger and not even know it. Her parents don't believe she is aware that Caulk is a convicted sex offender.

"She would never have left with him if she knew what kind of person he truly was," said Amber's mother, Kimberley Maloney.

Amber has been classified as an "endangered runaway" and the public has been asked to help find her.

"I'm hoping that if she finds out, or when she finds out, that she tries to find a way out, but does it smart," said Amber's father, Roger Westbrook.

"We have no reason to believe she was abducted," said Lakewood police spokesman Steve Davis. "We believe she went with him willingly."

Davis said that unlike typical runaway cases, detectives are actively looking for this missing teen.

The U.S. Marshals Service said Caulk was convicted in 2002 of sexual misconduct with a child in Pierce County, Wash., where he is registered as a sex offender. Caulk is currently wanted on warrants of failing to register as a sex offender in Yellowstone County, Mont., and failing to register as a sex offender in Lakewood.

Amber's family last saw her Tuesday, Sept. 25, when her stepmom dropped her off at school at the CEC Middle College of Denver, located at West 27th Avenue and Eliot Street.

Both she and Caulk were spotted the following day in Morrison, Colo.

Her parents said they had talked with her about hanging out with a 40-year-old man and told her there was only one reason that a man that age would be hanging out with a 16-year-old girl. They said she brushed off their fears.

"She told me she was capable of making her own decisions and was basically saying that she was making wise decisions. And we got into an argument about that and she left. She was not happy about the situation," Maloney said.

The teen hasn't contacted her parents since.

Amber's father confronted Caulk one afternoon to try to put an end to the relationship.

"I just tried to let him know that he needed to try to hang out with people his own age. He didn't have any reason to be hanging out with teenagers," said Roger Westbrook.

Westbrook said that he when he learned of Caulk's true name, he looked it up on the Internet and that's when he learned that the man his daughter was seeing was a sex offender with a history of assault on minors. That's when Amber's parents contacted police.

Caulk may be driving a red 1999 Mercury Cougar with expired North Carolina plates, or a dark green Volkswagen Golf, police said.

Recent tips to the police lead them to believe that they may still be in Colorado, but they could also be headed to California.

"I just want to let her know that we love her and we care about her ... and we're doing everything in our power to find her," Maloney said, adding, "Just please call and let us know that you're OK. Do the best that you can to get out of this."

Lakewood police describe Caulk as a white, 5 feet 7 inches tall, 140 pounds with hazel eyes and brown hair but may have shaved his head. He has a tattoo of a cross on his left hand and tattoos on his right arm, right shoulder, left finger and back. Both of his ears are pierced. One of his tattoos shows a Hawaiian god; Caulk is originally from Hawaii. He has been featured on America's Most Wanted.

Amber is 5 feet 7 inches tall, 160 pounds with blonde hair and blue eyes. Both of her ears are pierced and she has no tattoos.

Anyone with information about their whereabouts are asked to call the U.S. Marshals Service at 1-877-WANTED2 (1-877-926-8332), the U.S. Marshals Services Denver Office at (303)335-3400 or the Lakewood Police Department at (303)987-7111.

Additional Resources:

America's Most Wanted
National Center for Missing and National Exploited Children