My 24yr old son has large pimples on his chest, face &shoulder. we've tred all sorts of medicated soaps & visited the doctor once without any solut?

Soap won't work: I know you want the best for junior, and acne on the trunk (if that's indeed what it is) won't respond well to any topical therapy. A competent physician may begin him on something simple like tetracycline 500 2x/day perhaps with topical benzoyl peroxide and/or something else. This is likely to clear him; if not, it's his choice whether to undertake Accutane rx.