You cannot equate searching with going out, that is merely your interpretation. As the parents always went out alone only they know what they did and where. That applies to the trips away in the hire car too, nobody knows what they were doing as the magistrate refused to allow the vehicle to be bugged.
That applies to every searcher.
I believe the protocol is for police to organise named civilian volunteer searchers into groups who are allocated designated search areas each team led by a professional as demonstrated in the most recent search for a missing child in Edinburgh.
By 10am, 180 members of the public had registered at the North Neighbourhood Centre in West Pilton Gardens to join the search with hundreds more waiting outside to register.
http://www.itv.com/news/2014-01-17/community-unites-in-search-for-missing-mikaeel-kular/Tragic hunt: Members of the public assisting the police with the search in the Silverknowes area of Edinburgh
http://www.dailymail.co.uk/news/article-2705413/Mother-admits-punching-three-year-old-son-death-putting-body-suitcase-hiding-bush-sparking-massive-manhunt.html#ixzz5E4DstExK One can immediately see why the parents of a missing child are not encouraged to be 'hands on'. Had Mikaeel's mother been innocent of involvement in his death she was apparently in poor mental health so expecting her to conduct her own physical searching would have been most inappropriate.
As it stands, the fact she became a suspect who was subsequently found guilty of killing her little boy also shows how inappropriate it would have been.
Similarly, to allow volunteers to range in uncoordinated groups perhaps covering an area repeatedly while not touching on others at all is inappropriate.
Knowing who is searching where and when is essential particularly as at a later date a volunteer searcher could become a suspect.
In Britain we have this all down pat - and I'll guarantee it is likewise now in Portugal post 2007 - which is one reason why I find the constant moan about Kate and Gerry allegedly not searching being turned into such a big deal so risible.