The man was night fishing on the north-east coast at Tangle-Ha, to the north of St Cyrus, when he disappeared.
He was reported missing by another angler at about 3am this morning.
The Rescue Bond 1 helicopter and Montrose lifeboat are assisting with the search, as coastguard teams scour the shoreline.
A coastguard spokeswoman described sea conditions as "exceedingly rough".
Kevin Brown, watch manager at Aberdeen coastguard, said: "A search is still ongoing this morning to find this missing sea angler. Weather conditions are improving and although the wind in the early hours was gusting force 4 (13-17mph), there was a large sea swell of 2-3 metres.
"We'd always recommend that anglers check weather and tides before setting out and make sure they wear suitable clothing and a lifejacket.
"If you get into difficulty, or spot someone else in trouble, call 999 straight away and ask for the Coastguard."