LOL Ranked

Okay so Im playing ranked and my team already started out with a troll who afked. So as the jg I took control and covered the lane and continued to CARRY THE GAME up until we finally lost. What angers me is the fact that I went 20/10/10 with roughly 300 cs and yet the game is counted negatively towards my rank. I understand its a team game but when my team is wanting to /ff and Im still playing I have a problem. I had more than half of the teams kills, and I also destroyed EVERY single turret as well as all inhibitors. So my problem is the fact that even though I had a great performance in game, Im penalized for the terrible teammates who troll and afk.