Have posted this to Facebook (am a network rescuer so all my contacts are doggy or rescue people and will share). Please do the same and ask everyone else to as well.
When postering, put them especially in high pedestrian traffic areas - outside schools is a good one, people stop and are hanging around and kids are very observant and happy to help look out for a lost dog. Also vets for a WIDE area - email them a photo and phone numbers, outside POs, shops, in bus shelters/on bus stops etc. Sad to say this but if you have any "dodgy" areas with known problem households, flood that area too. A reward might help.
Keep the mobiles whose numbers you've put on posters with you and charged at all times - and put more than one number if at all possible. Ring dog wardens in neighbouring counties AND email description, photo and date/place of loss plus phone numbers to them all, your own included. Likewise local pounds and rescues. Get details of all those in your area from the Dog Wardens.
And good luck, hoping very much Thomas is found safe and well.... and nect time, with respect, NEVER leave your dog in a garden unattended. DOG THEFT IS RIFE, ALL MANNER OF DOGS ARE STOLEN, NOT JUST PEDIGREES AND NOT JUST TO SELL ON BUT FOR PUPPY FARMING, FIGHTING, BAIT FOR FIGHTING DOGS... YOUE DOG IS AT SERIOUS RISK.