19-year-old Jewel Manire and 20-year-old Khalil Gibson were killed when someone opened fire inside a parked Chevrolet Lumina on Hull Road in Camden's Fairview section.
Three other women were wounded, two critically.
The Citizens Crime Commission is posting $10,000 of the reward money and Manire's father, Demetrius Divine, an additional $5,000.
The Crime Commission will pay $7,000 for an arrest and another $8,000 if the suspect is convicted.
Anyone with information is asked to call the Citizen's Crime Commission's anonymous tip line at 215-546-TIPS.