The first answer is right, they grow a little temporarily because the blood stream focuses on the nips due to suction, but if you do it regularly -i.e. daily- they can grow permanently, but you'll have to use something stronger than nipple suckers, try some suction cups or nipple enlarger kits on ebay.
Another way to enlarge them faster is a nipple piercing.
I must say all the methods above give you so much sensitivity and are great for nipple play