It happened Friday morning on Hoffman Street in Valley Stream.
Police say the 19-year-old victim was approached by a man wearing a surgical mask over his mouth, who threatened him with a box cutter.
The victim handed over money, but the suspect slashed his face anyway.
The victim went home and called police. He refused medical treatment.
The subject is best described as being male, unknown race, 5'11" - 6'0" tall, stocky build, dark side burns, dark blue hooded sweatshirt, blue jeans.
Detectives request that anyone with information regarding the above crime to contact the Nassau County Crime Stoppers at 1-800-244-TIPS. All callers will remain anonymous.
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