The driver was parked in Southwick Square at around 11.15pm on Friday, January 18 when two young men, believed to be aged between 15 and 20, boarded the bus and demanded money from him, police said.
They driver handed over a quantity of cash and the pair ran off towards Southwick railway station, according to police.
Police describe one suspect as white, 5ft 7ins, of slim build and wearing a grey hooded top.
The second teenager was white, 6ft, of slim build and wearing a black body warmer without a hood and a light coloured long-sleeve top, police said.
Police said the pair were with a group of four teenage girls of a similar age.
Anyone who witnessed the incident or noticed a group of teenagers matching this description in this area should report online or call 101 quoting 1281 of 18/01.