The man was attacked as the bus he was riding on from Oldbury arrived at Dudley bus station.
Police have released two images of the women they wish to speak to in connection with the incident.
It took place on Thursday, September 15 at around 3pm.
A spokesperson for Dudley Police said: "We want to talk to these women after a man was assaulted on a bus from Oldbury as it arrived at Dudley bus station on Thursday, 15 September.
"Please contact us via Live Chat at http://west-midlands.police.uk or call 101, quoting 20/619411/22."