The victim was attacked in St Michael’s Alley, off Cornhill, in London’s financial district at around 3am on December 7.
Commander Jane Gyford, of the City of London Police, said: “This was a distressing attack on a young woman in the very heart of our city.
“We have identified from CCTV footage a man we need to speak to and if you recognise this person, it is vitally important you get in touch with police immediately.”
CCTV shows the man walking south on Norton Folgate in the Hoxton area at 2.30am.
He approached and spoke to a white woman with blonde hair and walked with her into Worship Street.
The man is described as white, possibly olive skinned, with brown hair and a slim build. He was wearing black trousers, a black blazer and a black scarf.
The police have urged the woman he approached to come forward as she may hold vital information which may help their investigation.
Commander Gyford said: “I want to stress, this woman is not in any trouble. She may be able to provide key information to us about the man who spoke to her.
“We would also like to establish that she’s OK. Anything she can tell us would be extremely useful.”
The CCTV shows the man at 2.45am walking along Liverpool Street into Old Broad Street and then along Threadneedle Street.
He is then seen outside a bar on Cornhill, the main road connected to St Michael’s Alley, where the attack took place.
CCTV still of the suspect City of Police wish to speak to regarding the rape of a woman near Bank. (City of London Police).He is then seen leaving the area and heading south of the River Thames.
He was last seen on CCTV at 3.30am walking over London Bridge and entering the area of Clink Street.
Anyone with information is urged to call police on 0207 601 2988, alternatively you can phone Crimestoppers anonymously on 0800 555 111, or visit http://mipp.police.uk quoting ‘Op Kaus’.