He also put his face inches from hers, offered to share his headphones and put his hand on her knee and upper thigh, authorities said.
Her attorney said she was touched more than 15 times during the flight.
A flight attendant returned to the row for drink service, and said she saw Camp's hand on the girl's crotch, the criminal complaint said.
Flight attendants moved Camp to another seat for the remainder of the flight, the FBI said.
Camp was arrested as he left the flight, and charged with abusive sexual contact, Oregon Live reported.
The teenager's father paid $150 each way for American Airlines' "unaccompanied minor service."
The airline's website said the service makes sure that a child who is traveling alone is brought on to the aircraft, introduced to a flight attendant, chaperoned during connections and escorted to the correct person at his or her destination.
According to the U.S. Department of Transportation, unaccompanied minor service does "not include constant supervision or entertainment during the flight."
Read more about what authorities said happened during the flight, as well as other flights where children and their families claimed that they were improperly touched.