A member of the public alerted authorities at about noon after the 16ft fishing vessel was two hours overdue.
The search is focusing on an area between Gourdon in Aberdeenshire, where it is understood the boat set off from, to Todhead Point and out in to the North Sea.
The RAF search-and-rescue helicopter from Lossiemouth, Montrose all-weather and inshore lifeboats, Aberdeen all-weather lifeboat, four local fishing vessels and coastguard rescue teams from Montrose and Carnoustie are involved in the operation.
Aberdeen Coastguard said the search had been suspended for the night because of fading light and fog.
It is due to resume at first light, depending on the weather.