Andrew Gallacher (20) of Kilwinning, was last seen in William Hill bookmakers, Main Street, Kilwinning around 5pm on Friday, June 20, 2014.
Andrew is described as approximately 6ft 2 inches in height, of medium build, with short brown hair and blue eyes.
When last seen, he was wearing white shorts, a white 'Hugo Boss' t-shirt with an emblem on the chest of the English flag, and blue Adidas 'Gazelle' trainers.
He was in possession of a blue bicycle when last seen.
Sergeant Allen Gow, of Irvine Community Police, said today: "Andrew has never gone missing before and it is very out of character for him to do so.
"He has not been in touch with his family for over two days now and concerns are increasing for his safety and wellbeing.
"I would appeal to the local community of Kilwinning, and indeed Ayrshire, for their assistance in our enquiry. If you have any information which might assist, please contact my team of community police officers on 101."