Roger Mole, who developed the system, said: "Being able to move part-exchange and traded-in vehicles is an essential part of getting large volumes of new or replacement vehicles into the marketplace.
The site will feature used cars that dealers can't sell; slow stock that would've gone to auction."
He expects dealer interest in the service to surge this month as the plate-change ignites the market in part-exchanges.
Buyers place bids over a period of one to 21 days, depending on the dealer's stipulation. Mr Mole said future developments would include fixed price classified ads. Dealers list vehicles free of charge and pay a commission fee of between 0-1.5% depending on the transaction price.
Mr Mole may add additional features to the site, such as insurance or accessories, though he ruled out finance. "We don't want to cut across services that dealers already offer, like finance," he said.