Juliette Edwards, aged 15, was last seen in the town at around 8am on Tuesday 8 November 2022.
Juliette is described as being five feet and one inch tall and of medium build. She was last seen wearing a dark blue coat, black trousers, black Nike trainers with orange on the sides. She was also carrying a black rucksack.
Inspector Sophia Keeling said: ‘We are concerned for Juliette’s welfare and we understand she may have attempted to travel to London by train.
‘I would urge anyone who has seen her or knows of her whereabouts to contact us.’
Anyone with information is asked to call 999, quoting reference 08-0305.