Like TeriM said, I would concentrate on feeding him canned food. Ditch the dry (especially Whiskas
). There are so very many reasons why wet is better, which you can read about here: http://www.catinfo.org/
Also, if you scroll down to the part about transitioning cats from dry to wet, there are tips on enticing a cat to eat. What was your kitten eating before you got him? You might have to go back to that until he adjusts to all the changes in his life.
And just so you know, you can
leave wet food out for free-feeding.