Bleach/gel whitening for teeth with enamel loss? is this effective?

Be careful: Bleaching is done with either carbamid peroxide or hydrogen peroxide. With thin or minimal enamel your teeth may be extrmely sensitive. Be certain to use Fluoride toothpaste. Toothpaste bleaching is relatively ineffective as compared to your dentist making custom fit trays with the proper bleaching agent. Toothpaste bleaching gets diluted with saliva and water. See dr. Oz.

Not really: Only enamel will whiten. If there is much missing, then you will not have much to whiten. You might need crowns to achieve the whiteness you desire. Unfortunately, veneers need enamel to bond too, and may not work for you. See a prosthodontist for evaluation.