I would suggest that you try these:

1. Facebook. This is an incredible way to find missing people. It's helpful also in there is usually a photo of every person with that name. Most people these days have a facebook page, and even if Donald doesn't, it's highly likely members of his family do. You may find him through members of his family who you can message on facebook.

2. 1. Searching the electoral rolls for the area he was known to live in, and any other areas where you think he may have moved to or lived in.

3. You could list him as a missing person. Depending on the circumstances, he may be looking for you too. You may find that you are listed as a missing person by him.. it's a possibility I suppose.

4. Take out a newspaper advertisement in the area he was last known to live.

5. This last one is a bit 'alternative', and it depends on whether you are open to this sort of thing.  You could visit a psychic. Ask around for a good one. Take a photo of Donald. He needn't be dead for you to find him this way, if the psychic is good.

I wish you the best of luck!

:-)