He is believed responsible for three robberies and one attempted robbery within the past ten days.
The most recent was Wednesday on the southbound A train at West 110th Street and Cathedral Parkway, where a rider was assaulted, robbed, and left hospitalized with facial injuries.
In each case, police say the suspect approaches a male victim, asks for the time, and assaults them as they provide the time.
The incidents have occurred on the Upper West Side, in Harlem and in Morningside Heights.
In one of the attacks, a victim was left with a punctured lung and broken ribs. Another suffered a broken jaw and broken eye socket.
Police have released surveillance video of the man they're trying to find.
Anyone with information is asked to call Crime Stoppers at 1-800-577-TIPS (8477).
The public can also submit tips by logging onto the Crime Stoppers website at http://WWW.NYPDCRIMESTOPPERS.COM or by texting their tips to 274637 (CRIMES) then enter TIP577.