Police said the woman had been walking near Railway Road when she became lost in the early hours of Sunday morning (July 14).
The woman told police she had carried on walking and had flagged down a passing vehicle for help.
Between midnight and 1am, a car stopped and the driver invited the woman into his car.
M6, M61 and M55 delays in Preston due to Blackpool Air Show and Lake District holiday traffic
Thunderstorms and heavy downpours of rain predicted to hit Lancashire as Met Office issues yellow weather warning
Man killed in late night crash on A6 Chorley Road near Blackrod
Two Preston men arrested after serious assault near Harris Museum
Real Housewives of Cheshire: former star of hit TV show set to visit Chorley boutique
According to the victim, the driver then made two stops whilst she was in the car, to deliver food to homes around the Railway Road and Corporation Street area.
Whilst she was in the car, the woman said she was sexually assaulted by the man before she was pushed out of the car in Clayton-le-Woods.
The distressed woman was found a short time later, at around 2.10am, by a member of the public in Ashdown Drive.
Detective Inspector Jason Richardson said: "This has been extremely traumatic for the victim who is being supported by specially trained officers.
"We know that this will be very concerning for people but we would like to reassure you that incidents of this nature are rare.
"We are taking this very seriously and have a team of detectives working on the investigation. Patrols have been increased in the area.
"We are in the early stages of our investigation and are asking for the public to come forward with any information that could assist us.
"If you live on or in the close vicinity of Railway Road and Corporation Street and received a food delivery between midnight and 1am, we would like to hear from you."
The driver is described as a man, approximately 30-years-old, potentially Middle Eastern in appearance, of a short and stocky build.
The woman said he had dark, curly black hair, a full beard and brown eyes and was softly spoken with no regional accent.
He was wearing a leather jacket and jeans.
Police are keen to trace anyone with information who may be able to help.
Detective Inspector Richardson added: "We are particularly keen to speak to a cyclist (pictured) as a potential key witness.
"The victim spoke to him on Corporation Street, close to the junction with Railway Road before she flagged down the car shortly after midnight.
"If you are the cyclist in the picture, we need to hear from you.
"You’re not in any trouble, but you could provide vital information to our investigation."
Anyone with information should call 101 quoting log number 180 of July 14.