The incident was reported at a residential building on 1st Avenue and Cooper Road in Peter Cooper Village on Wednesday afternoon.
The 86-year-old victim was waiting for an elevator when the suspect forcibly grabbed her chain and pulled it off her neck after a brief struggle.
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The necklace had a value of about $2,000.
The suspect ran away toward the East 14th Street and 1st Avenue subway station.
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).
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