The man reportedly took cash and cell phones from his victims between late May and early July.
The incidents have taken place on the No. 3 and C trains, as well as in the in station at 145th Street and Lenox Avenue.
Police say the suspect worked with another man, identified as 23-year-old Bruce Williams, who has already been arrested.
The outstanding suspect is described as a black male in his early 20s, approximately 6-feet tall with a slender build and brown eyes. The suspect was last seen wearing a gray hooded sweater, blue jeans and a Yankee baseball hat.
Anyone with information in regards is asked to call Crime Stoppers at 1-800-577-TIPS (8477).
WAKE UP WITH EYEWITNESS NEWS! Click here to download the WABC Eyewitness News Alarm Clock app from iTunes. or search WABC or 7online in the app store.
Get Eyewitness News Delivered