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).
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