It is unbelievable to me how haunting that must be. I can't even fathom the amount of pain that causes. I lost one of my cats many years ago. She was missing for 11 days. It was torture. She was found luckily and lived until she was 18. I am so sorry this happened.
The not knowing what happened is the worst. I can't help but think that he may have been taken by a dog fighting ring and used a bait dog. What a horrible thought. He may have looked tough, but he was a very submissive dog. I just hope that he was sold to someone is looking after him. He is nine years old now.
In tragic situations it seems our imaginations always play out the worst case scenarios. Somehow we just have to keep telling ourselves that not knowing is just that. We don't know. We can think the worst but we can only obtain some small amount of comfort by repeating that we will see them again and it will be a joyous occasion when it happens. I wish you peace and your boy happiness, light and well being wherever he may be until you are reunited