These people have teams of stylists who can do wonders with concealers and wigs. Hollywood magic also includes carefully controlled lighting and camera angles. In some cases, hair is recreated digitally during post-production. Even seemingly candid public appearances are often carefully choreagraphed events which celebs devote a lot of time to preparing for. The simple reality is that many of these people don't look as good in real life as they do on the screen and in pictures.
There are no effective hair loss treatments available only to the rich and famous. Just look at all the balding celebrities. These are men with plenty of money whose continued livelihood depends on their looks, and yet so many of them are still losing their hair.