The incident happened on a southbound 7 train last Thursday.
Authorities say the suspect exposed himself to the girl and and then rubbed up against her.
It happened while the train approached the 52nd Street subway station.
The suspect is described as a black man, approximately 30 years old, about 6 feet tall and 200 pounds, with dreadlocks.
Anyone with information in regard to this incident is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
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