The teen's parent told police that Jeremy Vague had the contact with the girl while she was on a sports team that he coached, said Lt. Justin Murphy of the Escondido Police Department, which is leading the investigation.
He said he had no other details because police had yet to meet with the family.
In a separate incident, another woman told authorities she was victimized when Vague was her Lyft driver in Encinitas, north of San Diego. Murphy said investigators would also be meeting with her and a female witness.
Efforts to determine if Vague has a lawyer were not immediately successful.
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The Associated Press does not generally identify people who say they are victims of sex crimes.
Vague was arrested today at his home after an 18-year-old college student said earlier that day that she was assaulted by her Uber driver in San Marcos, north of San Diego.
During the investigation, police discovered more possible victims, including two 19-year-old women in Escondido.
Both ridesharing companies are cooperating with authorities. Vague, who is married, worked for Lyft for nine months and Uber for three months, Murphy said.
As an Uber driver he had given 284 rides, according to information Uber provided at the request of police.
Court records show Vague pleaded guilty to a misdemeanor charge of vehicle burglary in Utah stemming from a July 2002 incident involving the theft of golf clubs.