Re: cat tearing out his hair
Oh he's adorable! I'm sorry that I've never heard of cats doing that. I Googled it and found that it could be caused by many different things including changes in environment. Try Googling it yourself and see what you can find. Perhaps you could also call some vets and get an opinion over the phone. Don't let anyone waste your money by rerunning the same tests. Explain that the tests showed no abnormalities and you believe that this habit is behavioral and not due to some skin condition.
Since this is probably due to the environment change of losing some house members, maybe you should make everything else as normal as possible, like his diet. If he had no problems with what you were feeding him before, I don't see a reason to change it. If he'll accept a bath, maybe try an oatmeal bath or some kind of shampoo to moisturize his skin. You can also get skin ointment to soothe his skin. If none of that works, you can rule out dry itchy skin.
You said his skin doesn't seem irritated, so I doubt that it's an allergic reaction. But just in case, try to brain storm any new chemicals you are using at home. Are you using any new lotions on your legs that he might be rubbing against?
Maybe he is lonely and he needs a new kitty companion. Be careful though, as this might make matters worse. You can offer to foster cats with some kind of animal aid or control center in your area, and see if he likes any of them before you adopt. That's if you can afford another pet. If you do decide to adopt another cat, he's more likely to get along with a female than another male. Just remember to spay and neuter!!!
I hope you find a solution for your very handsome kitty! What's his name, by the way?