The search continues during the weekend with a staff meeting about the missing woman who is in her 60s and was last seen at Vendelsjön, near Örbyhus in Tierp municipality.
On Friday, the police went into rescue mode and the Armed Forces and other authorities were called in.
From Saturday, Missing People will also participate in the search.
- We have already received help from the Swedish Armed Forces, sea rescue, mountain rescuers and civilians with rescue dogs.
Now Missing People is also joining the search, says Daniel Wikdahl, who is the police's press spokesperson and who participated in Saturday's staff meeting.
Mountain rescuer with quad bikes
The search effort includes ten specially trained mountain rescuers - with quad bikes and rescue dogs.
The search is complicated by the fact that you are not completely sure of the signal element.
- It is still not entirely certain what she is wearing.
But the clothing she wore the last time she was seen has at least not been found anywhere else, says Daniel Wikdahl.
The police do not suspect any crime at the moment.
Looking for electronic tracks
Police investigators are also looking for other clues such as logins in social media, says Daniel Wikdahl.
- We have searched for electronic tracks but she has not brought a mobile, iPad or similar.
We talk to people close to her and want to get in touch with more people.
We try to get an idea of what she usually does, says Daniel Wikdahl.
Those who have tips are asked to call the police on telephone number 114 14.