Very sad to hear that I have a cat to but he is not that young anymore but I can imagine how you must feel the best thing to do is looking outside when it is dark because a young kitten will hide in daylight because he is scared let us know when you find him!
The reason you don't let your cat outside is the average lifespan of an indoor/outdoor cat is only 3 years. An indoor cat can live to be around 18 years. Of course, some areas or neighborhoods can be safer, but you won't see many indoor/outdoor cats live to a ripe old age. I used to think as you, but all of cats died being attacked, or fighting with other animals. The oldest was only 8. No more indoor/outdoor cats for me. I would rather them live a long life. I would say you and your cat are lucky. After all, someone wins the lottery, but it's a long shot.
Our cats were indoor/outdoor cats and both lived pretty long lives. They both actually died of cancer of the jaw.
