Russell Sherwood, 69, left his home in Cilfrew, Neath Port Talbot in a silver Ford Focus at about 06:15 GMT.
He was headed to an address in Ewenny, Vale of Glamorgan but never arrived.
Officers believe Mr Sherwood reached Stormy Down and have been searching the area all day, assisted by the coastguard helicopter.
They will continue the investigation throughout the night.
Insp Andy Walbeoff said: "Some roads in Stormy Down were affected by flooding.
"Obviously we are concerned for his welfare - he has not going missing before and would always ensure a family member is aware if he is going to be late, but they have not heard anything."
Police are searching for a man who went missing after a car journey on Sunday morning.