Investigators said the 18-year-old victim had just gotten off the 4 train at the Fordham Road station.
The suspect followed her and then attacked her in a courtyard of an apartment building in the three hundred block of East 187th Street.
Police said the suspect used a boxcutter to threaten the victim.
Suspect was described as a Hispanic man in his 20s, 130-150 lbs, 5'3"-5'5", with black hair, and was wearing a blue/black and white striped shirt, black baseball cap, black jeans, and black sneakers.
Anyone with information is asked to call Crime Stoppers at (800) 577-TIPS (8477). You can also text tips to CRIMES (274637), then enter TIP577.
NEW YORK AND TRI-STATE AREA NEWS