SAN DIEGO -- A 34-year-old man who went to a La Mesa motel, apparently thinking he was going to have sex with a 17-year-old girl who advertised on craigslist, was robbed, and police arrested the girl and an accomplice, police said Tuesday.

The victim, whose name police withheld, met the girl at a room at the Heritage Inn, 7851 Fletcher Parkway, around 10:35 p.m. Monday, La Mesa police Lt. David Bond said.

After some brief sexual touching, the man gave the girl $100 for additional sexual services, Bond said.

About that time, a man in a mask came out of the bathroom with a knife, he said, and the would-be john fled and called police.

Police arrived and arrested Kevan Nicholas, 19, of San Diego, and the girl as they were getting ready to drive off, Bond said.

Nicholas and the girl, whose name was withheld because she is a juvenile, were arrested on suspicion of robbery. She was turned over to her parents at the La Mesa police station, while Nicholas was locked up in lieu of $100,000 bail, Bond said.

Police are looking for additional victims. Anyone robbed in a similar way was asked to call La Mesa police at (619) 667-1452.