Got a dog that will chase after a toy or you, but won't tug? Try this! Get a new plush toy and an old leash - the longer the better. At first show and tease the dog with the new toy, don't let him have it though! You play with it and then put it away. Do this for a few days so that he's very curious and wants that toy. When his curiosity is at its peak tie the toy to the leash, throw in on the ground and run dragging the toy behind you. Praise, praise, praise for the dog chasing the toy. Let him catch it every so often. Let him shake it and pull on it as you give a little resistance, then begin again. You may even let him fully win the toy and run off with his "kill".
*if your dog will destroy the toy or guard it be ready to trade up for the toy*
Keep playing this game slowly adding more resistance on the tug. When the tug behavior becomes more solid you can fade the chase part of the game. Once the dog is nuts for the toy and the game you two play with it you many begin to use it as a reinforcer for training. Make very sure that this special toy goes away up high where the dog cannot get it in between play sessions.