I have a one year old cat who has been missing for about 2 or 3 days. How and where do I start looking for him?

Put up signs and look around your neoghbor hood, calling for him.

Make some fliers, with photo and phone number. Knock on doors, show people a photo, ask if they have seen the cat and could they please check any garages/sheds to see if it has been locked in. Local vets, shops ask to put up a flier, contact rescues near by ask if any cat has been dropped off and contact the local authority environmental department ( or whoever pick ups road kill) to see if any cat has been pick up from the road

Post ads on craigslist and nextdoor. Check those websites for found cat posts. Put up signs. Let shelters, rescues and vets know you are looking for him and to call you if they get in a cat with his description. Get outside during the day and night (bring a flashlight). Most cats unless taken by someone cats are usually close to home so look around your house and ask neighbors if you can look around their houses and in their yards. Look every place a cat could possibly hide because hes probably hiding. Bring flyers with that you can give to neighbors so they know what he looks like and can keep an eye out for him. 

you could try putting ads outside asking people if theyve seen him