DENVER -- Jefferson County sheriff's deputies are looking for a man who impersonated a cop and pulled over a teen driver late Tuesday evening.

A 17-year-old girl told deputies that she was alone in her car, in the area of Coalmine Avenue and Pierce Street, when what appeared to be an unmarked police cruiser pulled up behind her around 11 p.m. The man in the cruiser activated the car's emergency lights so the girl pulled over to the side of the road, thinking that this was an official police stop, authorities said.

Just as the man got out of the car to approach the teen, another vehicle pulled in behind the patrol car and a woman got out and started walking toward them, the girl said.

The man seemed startled by this, retreated to his car and then drove off. The man has not been heard from since.

The woman told the teen that she stopped because she was suspicious about the situation.

Sheriff's investigators have not been able to identify the woman who stopped but consider her a witness. The only information known to investigators is that the woman drives a dark colored sedan, possibly a Mercedes-Benz.

The sheriff's office is urging anyone with information concerning the case to call (303) 271-5653.

This is the second cop impersonation case reported in the Denver metro area since Gov. Bill Owens signed a bill into law that makes it a felony to impersonate a police officer in Colorado.

Drivers who are suspicious of stopping for unmarked police vehicles can continue to drive to a busy parking lot and stop, police said. They may also call 911 from their cell phone to confirm the officer's authenticity. Drivers should remain locked in their car until the officer's identity can be confirmed, either by the officers' appearance, badge and identification card, or the appearance of a second, fully-marked car.