His red Ford Escort has been discovered at Tidduff, between Ballyheigue and Ballybunion.
No trace has yet been found of the 34-year-old man who has not been seen since March 24.
The car was found by the Garda sub-aqua unit after an extensive land search in north Kerry.
Also involved in the search were coastal and inshore rescue teams from Ballyheigue and Ballybunion, and a Shannon coast guard helicopter.
It is understood Mr O’Regan had been socialising in Tralee on Sunday night, March 23, and took a taxi back to Ballyheigue in the early hours of Monday morning.
He was last seen in his car in Ballyheigue village at about 4.30am, on March 24.
His family issued a heart-felt plea to the public for assistance in locating him.
His mother, Mary, said his children, aged between six years and 11 years, were crazy about him.