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 follow up: the trip wires will work a lot better if the on the sandstone floor. Maybe because it is a totally even flooring.
It works a lot 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.