The incident happened at approximately 10pm on Saturday, 21 November 2020 as the woman stood by the South African Royal Artillery Memorial in The Mall, SW1.
The suspect – a man who was seen riding a bike – did not speak to the victim before he assaulted her.
The victim, a woman in her 30s, reported the incident to police soon after. She continues to be supported by specially trained officers. Officers from Central West Sapphire Unit are investigating.
Detective Constable Hollie Jenkins, said: “It is really important that we identify this man as part of our investigation. If you recognise yourself or think you know who this man is please get in touch.
“It is vital that we track down the person responsible and I would urge anyone who can help to get in contact at the earliest opportunity.”
If you have any information that could help police please call 101 or tweet @MetCC and quote CAD7909/21NOV20.
Alternatively, you can leave information anonymously with the independent charity Crimestoppers by calling 0800 555 111