The beaten body of 18-year-old Julie Barnyock was found in a ditch near the Lansdale train station back in December 1993.
She was last seen at that train station on November 8, 1993 awaiting a ride home from her father.
On Friday Montgomery County District Attorney Risa Ferman used the 20th anniversary of Barnyock's disappearance to announce the re-opening of the case and to post the reward.
"Science has changed a great deal over the past 20 years. While there were certainly things done forensically to look at the evidence we've started from scratch," said D.A. Ferman.
Ferman said evidence from the case has been re-submitted for lab analysis, and a new team of detectives is now investigating the case.
"It's all hands on deck. We have every detective on the case and ready to go," said Chief Bob McDyre, Lansdale Police.
Investigators are hoping the reward will prompt someone with information not originally available to police to come forward.
"The reason we are announcing this reward is simply the hope that there is someone out there that has new information about the case. Perhaps someone who has been confided in by a person close to them and after 20 years it's time for them to release that information to us," said D.A. Ferman.
Anyone with information is urged to contact Montgomery County Detectives or the Lansdale Police Department.