this is hard to do, but a lot of fighting vs trynd comes down to positioning and timing. you must save stuns and slows for when he attacks you. you must aim to face him when he is going to slow you. dont forget, his slow lowers your AD, so wait till it ends to fight. Teemo is a good hard counter to trynd. Voli does well too if you know how to use him. (personal prefs, there are others who are good too)
you MUST run ignite and or exhaust - THESE ARE KEY COUNTERS to trynd. I cannot stress this enough. Exhaust is to stop his dmg on you, or a team mate.
Iginite is for finishing him off when his rage is almost done. dont do it too soon!