people who want to lose are going to find ways to lose
i suppose you can catch the most obvious trolls - the ones just running it down mid or following their jungler around and trying to outsmite him. but there is no way to force someone to try to win.
ive been seeing a lot of semi-trolling lately. supports taking cs from adc or players forcing bad teamfights and just running away without using abilities. you arent going to catch these type of trolls and even if you could, catching them is not the solution. they would just find other ways to throw games.
the solution has to be to come up with a way to make everyone want to win as much as possible. there should some way to detect and reward great effort or maybe bigger rewards for higher mmr. some kind of incentive for giving 100% is the answer.