Detectives are looking for a dog walker in a brown coat who may have witnessed a sex attack on the beach near the Shelter Hall last month.
A young woman reported being sexually assaulted shortly before 12.30am on February 12.
Three men from Hove – two aged 19, another aged 26 – were arrested shortly after on suspicion of sexual assault and are on conditional bail while the investigation continues.
Investigator Rose Horan said: “We would like to speak to anybody who can help us investigate this disturbing incident.
“Several members of the public, including a man in a brown coat walking his dog, were seen walking past the scene and we are particularly keen to get in touch with them.
“This was a distressing assault on a vulnerable young woman, who is being supported by specialist officers, and while we have arrested three suspects, work is ongoing to establish the full circumstances.
“If you can help, please contact police online or by calling 101, quoting serial 045 of 12/02.”