Cairngorm Mountain Rescue Team (CMRT) were called out to look for two people who had become disoriented on Braeriach on Thursday evening.
During the search they came across two other hillwalkers in difficulty, who were evacuated from the hill.
They were thought to be suffering from hypothermia.
Searches for the original two walkers were continuing on Friday, assisted by a Coastguard rescue helicopter.
Police said they are aware of the search.