Police are concerned that one of the people involved in a disturbance in Southwick may have sustained serious facial injuries, but has not come forward.
The disturbance happened at the junction of Whiterock Place and Station Road at around 10.15pm on Sunday, July 9, police said.
Police describe the injured person they wish to trace as a white man, aged 40 - 50, 5ft 10ins to 6ft, of average build, with an olive or tanned complexion and short salt-and-pepper hair.
At the time he was wearing a black t-shirt with green or tan shorts and flip-flops, according to police.
A 17-year-old boy hurt in the incident has been treated at Worthing Hospital for facial injuries.
It is feared the man may also require medical attention, police said.
Anyone able to name him or who knows of his whereabouts, together with anyone who saw what happened, is asked to email firstname.lastname@example.org or phone 101, quoting serial 1665 of 09/07.
Alternatively, call independent charity Crimestoppers anonymously on 0800 555 111 or via its website here.