Gardai are seeking the public's assistance in tracing the whereabouts of Stephen Sweetman.
The 18-year-old was last seen in Clonard, Balbriggan, Co Dublin, at approximately 4pm on Wednesday.
He is described as being 6’2” tall and of athletic build. He has short brown hair and brown eyes.
"When last seen Stephen was wearing a bright blue Canterbury hooded sweatshirt, navy Canterbury tracksuit bottoms, and brand new white trainers with fluorescent yellow markings," gardai said.
Anyone with information is urged to call gardai.