The young Océane, aged 16, has not been found since Saturday February 25.
The Charente-Maritime gendarmerie published a search notice on Sunday to try to find the teenager living in the town of Saint-Savinien (Charente-Maritime).
It was Océane's foster family who reported her disappearance.
According to the description released by the gendarmerie, the young girl with brown eyes and long, black hair is 1m60 tall and has a slim build.
Her attire at the time of her disappearance was not known but she was wearing gold glasses and a gray backpack.
Anyone with information about this disappearance is asked to contact the Saint-Jean-d'Angély brigade on 05 46 90 20 18.