At 4 months he's still a puppy. Don't put him on a line & whatever you do , don't just yank him in. If he's in the house call him when you feed him, always use the same command, here, come whatever. If he's kenneled use titbits when you have him out, cubes of cheese, pieces of sausage whatever turns him on. When you call him, crouch down & still facing him take big fast steps backwards holding out the titbit. Once he's 100% don't use the titbit everytime. When you call him use the nicest most friendly tone of voice you have.
As regards using a line, I have only used one on problem dog