Police: Man robbed teenager on train platform

Police are asking for help finding a man they say robbed a teenager on a train.
According to police, an 18-year-old apparently had his cellphone snatched out of his hands by a man onboard the southbound 6 train as it approached the Brook Avenue stop on Friday. 
When the victim followed the suspect onto the platform to get his phone back, the suspect allegedly displayed a knife and demanded more of the victim's property.
The suspect also took $80 from the teenager.
Anyone with information is asked to call Crime Stoppers at 1-800-577-TIPS.