A dog that won't chase an item you throw has no fetch instinct. You can still teach him to fetch but it is a command, rather than an instinctual game.
First you teach him to accept an item into his mouth. Use a word like "get it" or something that will still make sense once this turns into fetching later on. Have him sit, say "get it" and gently open his mouth and place a soft toy inside, like a rope chew (not something that might be uncomfortable in his mouth if he struggles).
Once he willingly accepts the item on command, start making him take it from you instead of putting it directly in his mouth. Gradually increase the distance he must move to take it from you. Eventually put it on the floor and make him pick it up.
Now start putting the item a step or two away from you and talling him to "get it". Once he picks it up, encourage him to come to you while holding it. Once he does this, gradually increase the distance he must come to you.
You now have a dog who fetches
But remember, in this case, the fetching is a COMMAND and you must not tell him to "get it" unless you intend to make sure he does it. As with all commands, if you tell him to do it and then allow him to disobey without consequences, he will learn that obedience is not necessary and will not bother anymore. This doesn't mean you should yell or punish him--just physically control him and bring him over to the toy and put it in his mouth. He will learn that the fetching will happen whether he wants to or not--and once he does it, he gets a treat!