I played Twitch all the time before the nerf. I was a little upset after the nerf but actually started playing him a bit more recently when my team needs a ranged AD character.
Your runes are fine. You definitely want to start with boots/prospectors blade. I always grab a vampiric scepter first for the life steal. Then grab IE then PD. Then counter build against the enemy. I usually grab AS boots, sometimes I'll go for the MR boots (man, boot names are drawing a blank atm, haha) depending on who the other team has.
But like Orphane said, he is one of the squishiest champs in the game and gets blasted down fairly quickly. You definitely want to go after a thorn or maw if that seems to be the case.
I still do fine with him in high ELO games, but yes there are better champs to pick than Twitch (all those OP champs.) huehuehue