Specialist officers from Dyfed-Powys Police, along with others from other forces, have been searching the area in and around Machynlleth since the beginning of October.
The force says the search areas identified during the course of the investigation were completed on Friday.
47-year-old Mark Bridger has been charged with murder, abduction and intending to pervert the course of justice.
He denies all the charges.
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An inquest is to be held into the deaths of four family members who died when their car was involved in a crash near Aberystwyth in June.
Cold and windy with sunny spells and showers of rain and snow.
The charity says the increase is partly due to people calling for help sooner, instead of attempting to rescue themselves.