I have to say that I can't see The Hobbit or Farmer Giles being appealing to a contemporary 12 year old. Many boys (and indeed men prefer factual reading) and I think finding stuff with subject matter that already appears is the key.
On the fiction side, I remember a not very academic boy cousin being addicted to the Lemony Snicket "Series of Unfortunate Events" at 12. They are nice and dark and introduce and explain a lot of vocabulary. It takes a while to build the stamina and the ability to get in to longer books so I would suggest going for page turners with that aim in mind even if they are not "great literature" . Another cousin read all the James Bond books at about that age. I read most of Agatha Christie in my preteen years and developed an addiction to detective stories.
Finally I wouldn't try to "make" him to read - youngstock are notoriously contrary beings. Try raiding the library for books that might be possible and forbidding him from reading them on grounds of unsuitability.....
