Area man Mark McGowan, 37, was last seen kayaking in the lough at 7.30pm on Monday evening.
His blue kayak was spotted by the Irish Coast Guard on Tuesday at Killowen Point, on the north side of the lough.
Dundalk Gardaí are co-ordinating the cross-border search operation, which was interrupted by bad weather early yesterday.
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Also assisting are the Irish rescue helicopter, Greenore coastguard, Kilkeel's RNLI lifeboat, the south Down coastguard team and the Community Rescue Service.
Meanwhile, the PSNI has appealed for anyone who might have information on McGowan's disappearance to get in touch.
McGowan is described as 5'7" tall, medium build, with a clean shaven, tanned complexion and short bleached blonde hair. He was last seen wearing a red jacket, blue jeans and white trainers.