Solent Group, which represented Citroen, Mazda and Nissan, has ceased trading.
Staff arrived for work on Friday morning to find the businesses in Portsmouth, which included the used car site Petworth Car Sales, still locked.
A message to customers on the group's website states: "It is with regret that due to adverse trading conditions, the directors have had to take the decision that the business must close.
"We are in negotiation with the banks to appoint an administrator and relevant parties will be contacted in due course, once this has been achieved.
"For staff, if you have any queries, please contact your line manager. "For customers, we apologise for any inconvenience that this has caused and if we are currently working on your car, or you are awaiting a delivery, please contact us by e-mail."