How do I defrost meatballs in the microwave?

I would not use the microwave. Instead, if you have a skillet that can hold all the meatballs, put 1 cup of water and a beef bouillion cube in the water. Add the meatballs and cover with a lid, and use a low to medium heat to gently simmer them until they thaw and heat through. Microwaves will make your meatballs rubbery. You don't have to use the entire bag, either. You can count out as many of them as you think you need per person. Once your meatballs have heated, you can remove them and use that cooking liquid to make your sauce with as well. If you are just determined to use your microwave, put the number of meatballs you want to use in a bowl or other dish. Add in a couple tablespoons of water, and cover the entire thing with plastic wrap. Microwave it on high for 3 minutes, then remove. Take off the plastic, and move your meatballs around, so that those in the center are on the outside, and those which were on the outside are in the middle. Recover with plastic, and microwave again for 3-4 minutes. That should thaw them fairly well.