TV is a time thief
 

Does the expression time thief exist in English?

time thief or thief of time makes sense in English. Very commonly you will hear wastes time. You can say devours time, but the meaning may be different.

Other equivalent expressions include "time sink" and "time drain".

(This use of the word 'sink' is similar to a 'heat sink' inside a computer: a device whose purpose is to pull excess heat away from components that generate it; the heat sink usually has an attached ventilator fan on the far side that uses passing air to carry heat away from the heat sink and out of the computer case. By extension, a "sink" can be anything that functions to pull something from the local environment and get rid of it elsewhere.)

More like at "waste of time" :)

In this sense it sounds fine to use "time thief" but it's not common and may not sound natural to some people.

As other have suggested, you can say "tv is a waste of time" or "tv is a time sink" to integrate more commonly used words.

Waste of time
 

I agree that "tv is a waste of time" would be by far the most common way to express this sentiment. The phrase "time sink" might convey the same meaning, particularly to a more technical person, but it is certainly not a common way to express this idea in English.