It happened around 6:00 Friday morning on the 700 block of West 10th Street.
Investigators say a 51-year-old woman was taking her 14-year-old daughter and a 15-year-old friend to the bus stop.
That's when an armed man approached from an alleyway and demanded the victims' property.
The suspect fled with a cell phone and the teens' book bags.
He is described as a male with light complexion, approximately 20 years old, and 5'7'' tall. He was last seen wearing a dark hooded sweatshirt, dark pants, a green traffic safety vest, with a ski mask covering his face.
Anyone with information is urged to call the Wilmington Police Tip Line at 302-576-3990. Tips can also be submitted to Crime Stoppers at 1-800-TIP-3333 or online at www.tipsubmit.com.