Police on Thursday issued images of two men they want to speak to in connection with the attack, which happened three-and-a-half months ago, shortly before 5am on Sunday, July 30.
Two people approached the woman as she left a station at Canons Park Underground station.
"They shared a brief exchange before the pair sexually assaulted her," said British Transport Police in a statement on Thursday.
"Detectives would like to speak to the men in the images as they believe they may have information that could help their investigation."
Anyone who recognises them is asked to contact the British Transport Police by texting 61016 or by calling 0800 40 50 40 quoting reference 81 of 30/07/2023.
Alternatively you can call Crimestoppers anonymously on 0800 555 111.