Specialist search teams and air support have been brought in to help find missing north-east schoolboy Liam Smith.
The 16-year-old has been missing since Saturday.
Police are now searching the village of Lumphanan where the Westhill Academy pupil was last spotted, getting off a bus.
Chief inspector Martin Mackay said: “Our inquiries continue this morning into the disappearance of 16-year-old Liam Smith from Aberdeen.
“Our investigation during the evening has established that Liam alighted from the 2.44pm bus which arrived in the village of Lumphanan on Saturday.
“When getting off the bus he then made his way north along Glen Millan towards the church at the top end of the village.
“Our searches have continued this morning towards the north end and we’ve been supported by specialist searches together with air support who are looking at the wider area.”
He added: “We are increasingly concerned for the wellbeing of Liam. A period of 72 hours have now passed since the 16-year-old boy has left home.
“This is very wintry weather which is causing us some concerns.
“We are appealing for any information from friends, from acquaintances, from people who think they’ve seen something to come forward.
“We’re looking to establish that members of the public that live in Lumphanan area can search outbuildings, check sheds, garages, any vacant property where someone may well seek refuge in this weather.”