Do anyone know what kind of font this artis use?

It looks like some version of an Extended Helvetica Neue. Possibly Light 33 Thin Extended. I'm 99% sure the connectors between the letters have been added since they don't appear consistently.

You won't be able to find real Helvetica fonts for free, but here's a great faux Helvetica that comes in all the versions - if you pick through it, you'll find a very light extended one. It's called Heavenetica http://www.kingston.ac.uk/support/mainsite/logos/f...

I don't recognise the font, but you can try at http://www.dafont.com/