She is identified as 10-year-old Qadr Williamson.
Officials say her foster mother last saw her on the 300 block of Glen Echo Road around 7:45 a.m. on October 21.
She is 5' 5" tall and was last seen wearing black pants, a black shirt, a blue hoodie and black sneakers.
During a Wednesday news conference, Chief Inspector Frank Vanore said the department often works closely with federal investigators on these cases.
Police think Williamson is with family or someone else she knows, but they have not been able to locate the child.
Anyone who knows where the child is should contact Northwest Detectives Division at 215-686-3353 or 911.