Some thoughts here.

A teenager who not only "punches his cat and slams it into the wall" but films himself doing it is a danger to everyone around him; I shudder to think what he may be like in years to come, when he will have more power over his life.

There are laws against animal abuse. I hope that is followed up.

YouTube was correct in taking down the video and rescinding his account. I should think they too could be liable.

Another person perpetuating the video... Unbelievable.