Sussex Police said they have helped return more than 100 abandoned vehicles to their owners who had used Gatwick First Parking before flying.
The firm, which is not a Gatwick-approved meet-and-greet parking company and has no relationship with the airport, appears to have ceased trading.
The website for Gatwick First Parking, which has been in business for 10 years keeping vehicles in a CCTV-covered secure compound, has been suspended.
Police said around 120 vehicles were found to be parked at various sites in Sussex and Surrey, and keys for cars left by travellers before they flew out have been discovered at a Surrey office.
Officers said around 30 sets of keys have been discovered for cars yet to be found, as they urged travellers to use official on-airport parking or off-airport firms registered with Gatwick’s approved operators scheme.
The news of the problem comes as millions of Britons prepare for the start of the summer getaway as schools break up.
Sergeant Darren Taylor said: “It’s essential that Gatwick Airport passengers use official on-airport parking, or companies registered with Gatwick’s off-airport approved parking operators scheme only, to avoid this sort of thing from happening.
“We’re carrying out further inquiries to locate the outstanding vehicles, and the owners of those vehicles will be contacted and kept up to date. Our priority is to find and return their vehicles to them as soon as we possibly can.”