Police say he followed the child into her apartment building in Pelham Bay on Wednesday, then reportedly began touching himself once inside.
The NYPD describes the man as having light skin, goatee, wearing glasses, in his 20's.
Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
The public can also submit their tips by logging onto the Crime stoppers website at WWW.NYPDCRIMESTOPPERS.COM or by texting their tips to 274637 (CRIMES) then enter TIP577.
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