Emma Tagliabue, 19, has been missing since the early hours of Sunday, 24 November when she was last seen in the Ealing Broadway area.
Emma is Italian, of medium build and about 5ft 6ins tall, with long dark hair.
She also uses the name Emma Drusilla.
She lives in Ealing and is believed to also frequent the Wembley and Clapham Junction areas.
Her family are very worried about her.
Officers are appealing for Emma to make contact with police or her family as soon as possible.
Anyone with information about her whereabouts is asked to contact police via 101, reference 19MIS046680.