A missing man faces a second night lost in bushland northwest of Sydney after police suspended the search overnight.

Police dogs and a helicopter spent Monday scouring bushland near Wisemans Ferry after Tiemuzhen Chalaer, 24, disappeared during a campsite party with friends on Sunday.

He is set to spend a chilly night - with temperatures expected to drop to 4C - after walking into rugged bushland sometime between 6.30am and 9am on Sunday with no supplies.

Friends of Mr Chalaer reported he was missing to police after he failed to return with them from the party near the Wheelbarrow Ridge Road track in Lower Portland.

Chief Inspector Garry Sims said the man's friends didn't realise he was missing until they returned to Sydney.

"It's one of those situations where everyone else was assuming he was with someone else, and it was only when people returned to their homes in Sydney they realised he hadn't returned," Inspector Sims told ABC Radio.

Police are concerned for Mr Chalaer's safety as he has a medical condition that requires medication.

He is described as having a shaved head with pale skin, dark brown eyes and a small moustache.

He is about 170cm tall and was wearing a brown chequered button-up shirt, blue jeans, black Adidas sneakers, a red scarf and a black leather jacket.

Police will resume the search at 9am on Tuesday.