Eoin Monaghan has been missing for 10 days and was last seen in the Knocknaheeney area of Cork city on Thursday, April 29.
Gardai were "notified immediately" when he went missing, the HSE said.
He is 5ft 5ins tall, 10 stone, with a medium build and has short brown hair and blue eyes.
He was wearing a black tracksuit with a purple and black- striped hoody when he disappeared.
"Urgent contact is being sought regarding his welfare and whereabouts," the HSE said.
Anyone with information is asked to contact the gardai at Gurranbraher Garda Station in Cork on 021 4946200 or any Garda station.