Detectives have had many calls from the public, and are urgently hunting the main suspects - said to be three or more black men with southern African accents. While the gang is still at large, women have been told not to go out alone after dark in Northampton.
Fears are growing that the gang may be inspired by South African "jack rolling", prevalent in the Nineties when gangs would seal off entire streets and rape every woman trapped on the street.
The five victims who have been attacked over the past fortnight - the youngest just 15 - have been approached in Northampton while out alone in the early hours of the morning.
Three were raped but two, including the young teenager, managed to flee from the men, who are thought to work in unison to abduct their victims.
DCI John Jones, who is leading the 30-strong Operation Harbour investigation, said: "A very kind member of the public who has asked to remain anonymous has offered a £500 reward and the force has matched that amount."
Posters have been put up all around Northampton warning women to be vigilant and try to stay safe. A team of 30 officers is now working on the inquiry, alongside the National Crime Squad and an automatic number plate-recognition team.
The attackers are described as tall, black men who drove a blue BMW car and a light-coloured Fiat Punto for some of the attacks. Mr Jones said officers still had an "open mind" on whether all five incidents were being linked.Reuse content