David O'Halloran, 18, was last seen outside Stirling University around 2am last Friday after a night out in Stirling. He was reported missing on Sunday.
Chief Inspector Gordon Dawson said: "We are continuing the search for David and have 40 trained search officers involved in this inquiry.
"Although not exhaustive we are concentrating the search in and around the university grounds area, which is where David was last seen.
"I have utilised the expertise of Mountain Rescue and the International Rescue Corps. We are also appealing to the public to check garden sheds in the event David has taken shelter there."
David is described as 5'5" tall, brown hair with blond highlights which is short at the back and longer on top, of slim build and was wearing a white T-shirt with a black and green checked shirt on top. He was also wearing black slim-fit jeans and black trainers.
Chief Inspector Dawson added: "We are stopping motorists passing the area of the university and appeal for anyone who may have seen David, or who knows where he is, to contact us."