The driver was an Asian man, aged in his late 20s. In the passenger seat was a white male, described as being tanned, aged in his early 20s.
The passenger - who was known to the woman - got out of the car and pulled the woman into the back seat before getting in with her and all three then drove away.
On the morning of Tuesday, 22 August the woman was found in the West Ealing area and was helped by a female member of public. The victim would have been in a distressed state and required clothing and also medical treatment.
Officers would like to speak with the member of public who assisted, who was aged in her late teens to early 20s; she spoke with an Irish accent and had purple hair.
Any witnesses or anyone with information is asked to contact Ealing CID on 07825 114 094 or 101 or Tweet @MetCC.
Information can also be reported anonymously to Crimestoppers on 0800 555 111
A 21-year-old man was arrested in connection with investigation and has been bailed to return on a date in mid-September.
Enquiries continue.