Sussex Police said officers are investigating after an incident was reported outside the Pryzm nightclub in West Street, Brighton, at 4am on June 29.
"A 25-year-old man and a 20-year-old woman from Brighton were assaulted and both required hospital treatment for minor injuries,” a police spokesperson said.
“Police arrested a two men aged 19 and 21 from Luton on suspicion of causing grievous bodily harm. They have been bailed, pending further investigation.”
The police are now appealing to locate a teenager in connection with the investigation.
A spokesperson added: “Officers wish to trace Harley Graham, aged 19, as they believe he may have information which can assist with the investigation.
“He is believed to have links to Ampthill in Bedfordshire, as well as links in Luton, Stopsley, and central Bedfordshire.
“Anyone who knows his whereabouts is asked to report it to Sussex Police online or call 01273 470101 and quote serial 217 of 29/06.”