Officers were called at 12.12pm on Saturday 12 December 2020 by a woman to report she had just witnessed three men assault and rob another man in Stream Walk.
Officers attended the scene and following immediate enquiries were able to identify the suspects and arrested three men on suspicion of robbery.
But the victim had left the scene in the direction of the harbour.
Detective Inspector Cara Ferguson said: ‘We would like the public’s help in trying to locate the victim in this incident, to ensure he is safe.
‘We believe he is a young man. We appreciate this isn’t much information but we really would like him to get in touch, or anyone knows him to get in touch.’
Anyone with information should contact Kent Police on 01843 222289 quoting reference 12-0499.