With her son missing for 21 days as of Friday, a Bronx mother pounded the pavement again to look for him.

"I will turn every rock and every stone until he is found," said Angela McBride.

The cold, wet weather didn't stop McBride from posting and handing out fliers. She last saw her 15-year-old son, William Dickerson Jr., on Sept. 11 before he went to school at Validus Preparatory Academy on Bathgate Avenue. He never returned home.

Police traced his MetroCard, which was last used on the Bx41 bus on Webster Avenue. Surveillance video from inside the bus shows Dickerson. His MetroCard shows no further activity.

Dickerson left for school wearing a backpack, purple Validus Prep shirt, black shorts and white sneakers. The video from the bus shows him without a backpack, and a white T-shirt is over his school shirt.

"William, come home," a tearful McBride said as she spoke with News 12. "Please, if anybody knows anything, please come forward. I'm not trying to bury my son."

McBride said although she has had many sleepless nights since her son's disappearance, she is trying to remain strong for her two children at home.

Anyone with information about the teen's whereabouts is asked to call Crime Stoppers at 1-800-577-TIPS.