Cat Dumbo missing

One of my cats, an almost one year old male named Dumbo has been missing for four days now. I've just returned from the garden - searched for him everywhere but couldn't find him. I'm worried and sad. On Saturday I opened the window to the garden for them for the first time since I adopted them last summer. They were hesitating for an hour or two but then he finally decided to step outside. He climbed down the pile of wood to the lawn and that's when I last saw him. It didn't occur to me that being so shy he might have the courage to go anywhere farther than a couple of steps from the window. But either he had the courage or got scared and hid somewhere. He was so small and thin, barely over six pounds of weight. I'm worried what might have happened to him if he wasn't fed for four days now. Please send positive energy his way.. I'm still hoping he will show up.