I was thinking about some things that happened to me and some stories of some night creatures talk about and this question came to my mind
Can a thougtform use the negative energy as a life source? If a thoughform lived of negative energy of humans and the dark beings then that creature could not only get strong eneough to make enemies run away in fear because it would get more powerful everyday but it could live forever too.

They can and they do, a study of the Qliphoth would reveal this.

wait a minute I havent read so much the qlipoth are called demons or created demons
is this so?

The Qliphoth are shells of negative existence. For every thought, action or anything for that matter created, there exists its negative aspect.
The Qliphoth define and evolve themselves through the funneling of further negative energies created.

In my opinion I would be cautious about it.
There is a possibility you can become possessed (not like in the movie) by negative spirits or energies.
IMO you could also pick up negative vibrations that can bring you certain diseases (eg cancer etc).