I have an tripwire enderman farm as shown here:
At initial setup, the tripwires did activate(with the click sound) and I also did check that the tripwires did extend the pistons but after awhile, the tripwires suddenly deactivates and when I test it out, the pistons does not extend.
My tripwire enderman farm is very similar to the one in this video:
EDIT: Oh, too bad this question is closed. Short followup: the trip wires will work alot better if the on the sandstone floor. Maybe because it is a totally even flooring.
EDIT2: Since from the previous edit, I felt guilty for not sticking to my problem initially so I changed half a layer of my design back to tripwires and this is the result : It works alot better with no blocks under the trip wire hooks as Kevin Reid suggested.
EDIT3: Moved all the edits below the question and also.. In my conclusion, from what I can see tripwires works the best when there is either a block under every tripwires and tripwire hooks or no blocks at all under each of the tripwire components.