Keir Earl, 13, and Colese Marsden, 15, were reported missing from an address in Wick at around 1.30am on Friday.
Colese is described as 5ft 2in and of slim build with a tanned complexion. She has long dark hair with dyed blonde tips.
When last seen she had a brown blanket around her.
Keir is described as slim with a pale complexion and short red hair.
He was last seen wearing a red football top.
Anyone with information about their whereabouts is asked to phone police and quote reference number 0204 of 24/08/2018.