Pulling fur out?

Hey everyone.
Im new.
My eldest cat, Simba, has anxiety he's been losing weight and pulling out his fur. He also has fleas. I have gotten flea medication for him and My two other cats Lucky and Caprice.

What else should i do to help him get back to his old fat self?
Ive tried to feed him wet food, a treats, also a bit of human food but nothing seems to work.

First, a belated welcome to TCS!     Second, an apology that you didn't get a reply sooner.  We usually are much better than that but somehow it seems your question fell through the cracks.

The best thing you can do to get Simba back to health is to take him to the vet for a check-up.  Losing weight with no clear reason always calls for a vet visit to see if there is an underlying problem.    You're definitely doing the right thing in treating the fleas and giving him more tempting food but it's best to take him to the vet at this point.  Simba might have a dental problem or one of the diseases that older cats are prone to, such as diabetes or kidney disease.  

BTW:  we love photos here at TCS.   When you get a chance, post some of Simba, Lucky and Caprice so we can admire them!