The New Zealand Police Missing Persons - http://www.police.govt.nz/service/missing-persons/
This site no longer lists Quentin's profile as since the inquest in 2014, he is considered deceased.
In New South Wales, Australia, there's http://www.missingpersons.justice.nsw.gov.au/ which has some excellent information and support
Quentin has also been on the Australian Missing Persons database since 1994.
The Salvation Army carried out a search for him at our request - unsuccessfully. They are a helpful and resourceful organisation to contact: www2.salvationarmy.org.uk/familytracing
In the UK, there is the Missing Persons charity: www.missingpeople.org.uk
A joint site to help people searching for loved ones - www.look4them.org.uk/
There are many other sites worldwide - too numerous to mention.