Const. Yannick Ouimet said 15-year-old Sabrina Beaubien was last seen before she left her home in Montreal's Ahuntsic borough at about 10:30 a.m. on Jan. 18.
Police are concerned for the safety of the young woman.
Beaubien, who is French-speaking, is about five feet seven inches and weighs 105 pounds.
According to Ouimet, the teen was not carrying any ID or bank cards when she left home.
She has brown eyes and brown hair, with red highlights.
She was last seen wearing a black jacket, a grey sweater and black pants.
Anyone with information about Beaubien is asked to call 911.