Close Call Group of Teens surrounding Car

On my drive home from work today, May 8, 2014 at around 4:15 I drove on Hartsdale from Hillen to Loch Raven near Northwood School. 4 or 5 teens were walking on Hartsdale taking up a lot of the road. As I got closer, a tall, African American girl, flagged me down and crossed into my car's path. She placed her hands on the hood of my car and yelled, "M'am, Get Out of the Car! Get Out of the Car! This is a stick up!" I didn't look to see if anyone had a weapon. She began to walk to my open driver's side window and I hit the gas.  I have called the police but since I left the scene unscathed I don't know if the police will follow up. Posting here seemed the best way to get the word out to our community about this activity.