The victim, a woman aged 45, was pulled over after being followed by two men in a silver car with blue flashing lights in the Gleadless area of the city at 12.55am on Saturday.
She was told to get into the car and was driven to an area off Spotswood Place. The woman received minor cuts to her chest before she was able to escape and contact police.
South Yorkshire Police said the driver was wearing a high-visibility jacket and the car is described as possibly a VW Golf with blue flashing lights in the front grills.
Det Insp Graham Stead, the investigating officer said: “We appreciate this is an extremely concerning incident and we can assure members of the public that we are following a number of lines of enquiry to find and arrest these men.
“We are treating this incident as an utmost priority and while we are in the early stages of the investigation, we have a large number of resources allocated to this case.
He advised members of the public to be vigilant and added: “If you are requested to stop by a police vehicle, the car will be appropriately marked and if you are in any doubt pull over in a safe and public place and contact 101 or drive to your nearest police station
“Always ask to see identification and always call 999 in an emergency.”
The two men in the car are described as being aged between 40 and 50, of mixed race and speaking with foreign accents.
Anyone with any information is asked to call police on 101.