Have you tried putting a blanket down on the floor? Are his legs and feet covered? It migt be a texture thing. Maybe get a really eye catching toy, maybe his favorite and place it just out of reach. This might encourage him to get to it. This worked on my nephew. My daughter would move in her crib but never crawl. We did tummy time and lots of other excersizes. But she stood up at 9 months and ran across the room.
If all he will do it crawl on the bed, be excited and watch him so he doesn't crawl off. He will eventually crawl or stand up and walk.