CCTV images of a teenager at a railway station on the night she disappeared have been released by police.
Police have released CCTV from Ipswich Station
Natasha Coombs, 17, was travelling back by train to her home in Dovercourt, Essex, from Ipswich, Suffolk, when she went missing on 27 July.
The CCTV images show Natasha standing at Ipswich Railway Station just prior to her catching the 2242 BST train towards Manningtree.
There have been no confirmed sightings of her since.
Natasha had travelled to Ipswich that night to meet friends for a meal in Cardinal Park.
She rang her parents at about 2240 BST to say she was on her way home.
She was due to switch trains at Manningtree but her phone disappeared from the mobile network.
Police said there were no CCTV cameras on the train and the cameras at Manningtree station were not working.
Officers believe that Natasha may have been upset over a recent relationship break-up.
Natasha Coombs went missing on 27 July
However, there is no indication she was planning to disappear as she had no additional clothing with her and wears disposable contact lenses and brought no spares.
Supt Gareth Wilson, heading the investigation, said: "If anybody is able to help us by providing information about Natasha's whereabouts, I urge them to contact police immediately.
"In particular, I wish to make a direct appeal to Natasha herself to get in touch and let us or her family know she is okay."
Natasha is white, 5ft 3in and slim. She has brown hair with highlights and at the time of her disappearance was wearing a purple, sequinned top, a multi-coloured ra-ra skirt and a white jacket.
She was also carrying a black, furry handbag.
Searches for Natasha are focusing on the Manningtree area, where it is believed she may have got off the train from Ipswich.
On Thursday, Natasha's parents, Gary and Joanne, made a plea for help finding their only child.
Mr Coombs, 48, who works in Norwich, spoke of the "unimaginable pain" he and his 40-year-old wife were suffering.
Anyone with any information is asked to contact Essex Police.