Overview
- Alexis, also known as Lexi, is believed to have travelled from Northampton to London at about 10:30pm on Friday, August 15.
 - Police say she was seen in central locations including Leicester Square and Marble Arch, as well as the Heathrow area.
 - Her last known location was Tottenham Court Road on Saturday, August 23, according to the appeal.
 - The teenager is described as around 5ft tall with a slim build and long dark hair.
 - Officers released a photo and said concern for her welfare is increasing as the search continues.