I do hope you find the little one soon. Perhaps you will take the advice below although I appreciate you have already done some of the suggested things.:-
Advertise, advertise, advertise with picture and details with contact number, hand out to neighbours and anyone you see. Put up in local shops, pubs and supermarkets. Stick to all local lamp posts, best to laminate or put in plastic bags. Also put one in your and friends cars - it amazing how many people see them this way. Make smaller flyers and push through every letterbox on your streets and the surrounding area, 1000 if necessary. It is a good idea to offer a reward. Round here someone advertised in a shop for 6 months and then someone who lived very near the owner saw the advert and realized it was the cat they had taken in.
Knock on doors and ask neighbours to check their sheds and garages WHILE YOU WAIT … at least a few hundreds yds each way and also remember the roads surrounding. it's surprising how many people say they will check but as soon as the door is closed they forget.
Register the little one lost at all vets/catteries/rescue homes within a 20 mile radius. Follow the link and click on the map to find rescues in your area catchat.org/adoption/index.html
Leave food out and a toy out & an unwashed item of your clothing
Put the contents of your hoover bag on your garden - it’s full of smells that they will recognise and if doesn’t bring him directly to your door will at least hopefully keep the little one in the area. Alternatively if you have a litter tray that has been used put some of the used litter on the garden as this will have familiar smells in it.
Ask the local children to look - they are great for knowing all the local hidey-holes and love helping. Also have a word with your local post-person and milk man if there is one that delivers in your area. Also try and enlist the help of people walking dogs as they tend to go “off road” in the fields and parks.
Ask the local radio station to announce he’s missing and give out a contact number
Put an advert in the local paper. Someone in our town advertised for 9 weeks and then got the cat back
Contact your local environmental services dept (bin men) they keep a log of all animals picked on the roadside ... I know this is not a pleasant call to make and hopefully it will come back as negative.
Go out after dark when it is quieter with a friend / partner and walk round the local area gently calling every so often (give him a chance to answer you). Keep talking as you walk round that way if the little one is in the area they will hear you.
When you talk to vets and rescues, ask them about any known local feral colonies and where they are based. If the little one has been missing for more than a few days s/he might have wandered further afield and might be “hanging round” near a colony for security and company.
Finally have a look at these sites:-
http://www.lostcatsbrighton.org.uk/html/advice.htmlwww.animalsearchuk.compurrsinourhearts.co.uk/index.php
mymoggy.com/ contact Sue at mymoggy.
thehovel.com/bb/index.php?f=28&ppage=20&sort=lastpost&order=DESC
nationalpetregister.org
soyouhavelostyourcat.co.uk/#1
petsearchuk.org.uk/
amissingpet.co.uk/lostandfound.html
animalsearchuk.com/
pet-rescue.org.uk/forums/index.php?showforum=308
lostmycat.org/index.php
animalrescuers.co.uk/html/lostfound.html
foundandlostpets.co.uk/
1.freewebs.com/pettalk/missingpetsbulletinboard.htm
petsmiles.com/v1/found.php
Also don't forget to check ad websites, such as.....
friday-ad.co.uk
adtrader.co.uk
uk.freeads.net
classifieds.co.uk
Hopefully your little one has just got itself shut in a shed somewhere.
It is very important when you get your little one back remember to remove all the posters and inform all vets / rescues / websites etc that they are home.