At around 9pm on Thursday 9 November 2017 the victim was cycling along Halstow Way when a car, described as being dark black or blue, pulled up alongside him.
It is alleged a man exited the vehicle holding a large knife. He is said to have demanded the bike and then rode off on it.
The car drove away towards Brookfield Road.
Descriptions of bike and suspect
The bicycle is a grey and green Specialized Rockhopper mountain bike. The word Specialized is in white letters.
The suspect has been described as being black, aged in his 20s and tall. He had a cut to his lip.
Call with information
Officers have carried out a number of enquires including house to house and reviewing CCTV in the area.
Anyone who can assist the investigation is asked to call Kent Police on 01843 222289, quoting ZY/055271/17.
Alternatively, contact Kent Crimestoppers anonymously on 0800 555111.
Kent Police 12 November 2017