The person driving the vehicle struck and killed 16-year-old Faith Sinclair on a Sharon Hill street on Sunday night.
The Citizen's Crime Commission is now offering a $10,000 reward for information that leads to a conviction.
The Ridley High School student's uncle pleaded for help.
"For those of us privileged to know Faith, we were truly blessed. We ask that anyone with information regarding this tragic incident, please call the District Attorney's office of Delaware County," Frank Daly said.
Investigators are asking all manufacturers of Mercedes replacement parts to be on the lookout for someone looking for repairs, particularly for that passenger side rear view mirror. Investigators are also asking all salvage yards and private repair shops to do the same.
The DA also says a witness may have seen a passenger in the Mercedes.
If so, police want to talk to that person now.
"As time passes we begin to analyze this case very much differently with respect to that passenger; we urge that passenger to come forward," Delaware County DA Michael Green said.
In addition to the rearview mirror, police say the car will have significant front-end damage.
If you can help the case, call the Citizen's Crime Commission at 215-546-TIPS.
