The 22-year-old woman was visiting the capital when she was told to get out of a taxi after her friend had been sick, in the early hours of Sunday, 3 June.
The Metropolitan Police said she had “no recollection” of what happened next.
Officers were called to a hospital in South London, where the woman had sought treatment for “vaginal injuries.”
CCTV footage shows the woman and her friend walking with two unknown men in Haymarket, near Trafalgar Square, around 3am.
One of the men can be seen carrying the woman to a nearby doorway, where it is believed she was raped.
Officers from the Child Abuse and Sexual Offences Command (CASO) have launched an investigation.
They released a CCTV image showing a man who is being sought in connection with the attack.
A spokesperson for Scotland Yard said: “Officers spoke with the woman – an American national who was visiting London on holiday – at the hospital.
“She recalled being told to get out of a taxi in the early hours of the morning after her friend had been sick, but had no recollection of subsequent events prior to waking up and seeking treatment for her injuries.
“Analysis of CCTV showed the woman in the company of her friend and two unknown men in Haymarket, W1 at around 3am on 3 June.
“One of the men is seen to carry the woman to a nearby doorway, where the available evidence suggests she was raped.”
Anyone who recognises the man is asked to call officers from CASO via 101, quoting reference 7720june03 or to remain anonymous, call Crimestoppers on 0800 555 111