An escaper is somebody who leaves a game when they are losing. Every go server has them.
Best thing is to leave them a nice message. Sometimes people get upset and leave, but if they get a nice message, they'll cool off and be willing to finish the game later. It's also possible that they had connection trouble or their client crashed.
OK, so they're almost definitely really running away from a loss. First, don't stress about it. Whatever you do, don't start screaming in a chat room about it. It won't help, and it will annoy other people. What does have to be done is for the server to know that the person escaped, and that happens automatically.
The first person to leave a ranked unfinished game (whether by closing the window, logging out, or disconenction) is marked as escaping that game. You can do this a few times without any penalty, but do it too much and you will start losing the old unfinished games by forfeit. If you keep escaping then you become a "chronic escaper" meaning any ranked game that you escape will be instantly forfeit.
What does this mean to the people victimized by an escaper? It means that if the person really is an escaper, just wait. You will get your win. Yelling, screaming, complaining to the admins, won't help, only waiting will help.
Very, very few people escape only once or twice. If somebody escaped from your game because they can't stand to lose, then they'll do it again next time they're losing, and once they do it enough, you will get your win.
The goal of the server is not to punish anybody. It is to make sure that you can adjourn a game from time to time with no problem, and also to make sure that players who walk away from lost games are counted as resigning them. To perform that goal, every time that you are the first player to leave a rated unfinished game, the server will put you into one of three groups:
Note that only ranked games are considered for escapes. Escaping from an unranked game is considered to be an impolite way of saying "I resign."