My dog has always been a fussy eater but the last couple of months he can not eat enough and is even stealing food - seems to be loosing weight - has been wormed etc - any ideas / anyone experienced this ?
No never experienced this GILL, but I'd do what I always do when I'm worried about my dog's health for any reason, 'phone the vet and make an appointment.
My old dog had a similar problem, kept eating yet losing weight, turned out to be a kidney problem, if I remember correctly. He was 14 at the time so the outcome wasn't good. So as Jules said get him to the vet.
Hyperthyroidism and/or kidney problems I would guess. Please take him to your vet asap as if this turns out to the case it is serious and he needs help.