Hi Nicky,
Sorry to hear Misty has gone AWOL.
My main piece of advice is POSTERS, POSTERS, POSTERS - get as many posters and flyers out as soon as you can. The more posters the more chance there is of someone actually reading them. Also know on your neighbours doors (for at least 10 houses both sides of the street either side of your house) and ask them to let you check their sheds and garages. DO NOT assume if Misty is shut in somewhere he will rush out of an open door .... sometimes when a kitty is scared and frightened it very well may hide in a dark corner rather then coming out.
Good luck and fingers crossed Misty will be back home soon.