A 15-year-old California girl missing for more than a week may be with an "armed and dangerous" sex offender who disabled his ankle monitor and cannot be found, authorities told FoxNews.com. 

Patsy Lopez, of Bakersfield, was last seen July 20 at 11 p.m. Police suspect the child, who is 5 feet 2 inches tall and weighs approximately 120 pounds, is in the company of John Gonzales, a 37-year-old registered sex offender who is currently at large. 

It's not known whether Lopez is with Gonzales or whether she was the victim of an abduction. Sgt. Joe Grubbs of the Bakersfield Police Department said Lopez is currently classified as a "runaway" because police determined she left her home willingly.  

Lopez is considered at-risk because of her age and an unknown medical condition. 

"There are additional concerns with this because of the possibility that she's with this man," Grubbs told FoxNews.com on Tuesday.

He also said runaway cases "happen all the time" in Bakersfield. "Most of the time, they come home ... it's an overnight deal," he said, adding that he deals with hundreds of similar cases on any given week.  

The FBI announced yesterday that it recovered 105 teens -- mostly runaways -- in a 72-hour nationwide sweep intended to rescue children forced or coerced into the sex trade. Ronald Hosko, assistant director of the FBI's criminal division, said "Operation Cross-Country" -- launched Friday -- included sting operations in 76 U.S. cities that resulted in the arrests of 150 pimps.

Hosko said law enforcement refers to these young victims as "children with a void." Once the pimp identifies that void and makes every attempt to fill it, a dependency between the child and the perpetrator develops, Hosko said.

He added that the most vulnerable victims forced into sex trafficking range in age from 13 to 16. Most of the children come from either foster care homes or are considered runaways.

Lopez, who was last seen wearing a pink shirt, green shorts and sandals, is Hispanic with brown hair and brown eyes. Gonzales is described as 6 feet 1 inch tall, with black hair and brown eyes. 

Anyone with information on the whereabouts of Lopez or Gonzales is urged to call the Bakersfield Police Department at 661-327-7111.