The 19-year-old victim was cycling home from work at about 3am on Sunday 8 November.
He was in Ployters Road, near the junction with Brockles Mead, and saw a group of men coming down a cycle track behind factories in Perry Road.
One of the men approached him and punched him in the face in what is believed to be an unprovoked attack. The group then walked off. 
The victim needed stitches to his lip.
Police have been carrying out enquiries in the area and reviewing CCTV, and are looking to speak to anyone who was in the area at the time. As it is an industrial area, there may be people who were going to and from work.
The suspect was described as white, aged in his early 20s, with very blond, short hair and blue eyes. He was about 6ft tall, of slim build and wore dark trousers, a dark jacket and a light coloured top.
Anyone with information is asked to contact Harlow CID  by calling 101 and quoting reference 42/182919/20.