Police are asking for the public’s help in finding a man they say robbed a teenager in the Bronx.

According to police, it all happened Friday onboard a southbound 6 train as it approached the Brook Avenue stop.

The 18-year-old apparently had his cellphone snatched out of his hands by the suspect.

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

He ultimately made off with $80.