I think people are expecting far too much of this show, its a zombie film drawn out over a series, everyone in zombie films is fucking stupid, they all die because they do something stupid, if you sit there looking for flaws you are easily going to find them, just switch off and go along for the ride, stop watching with a critical eye, the genre does not stand up to hard criticism and you are always going to be left feeling short changed if you dig too deep.
As a cynical veiwer I think of myself as a supposed hard case, yes like to think I would of fucked the kid off for dead by now, at least thats what I say sat watching it, but in that reality, I cant say what I would do, in fact I'm pretty sure I wouldnt be so cold in reality, so I think its very realistic that they continue to look for her, its what people do, its lost causes and particularly kids, people go out their way when its a kid in trouble.
If you think about it as well, if they give up on her, without even knowing what happened to her, well thats it for them as a group, they whole thing falls apart, if they arent willing to go the extra inch for each other in this circumstance then they are fucked, they cant trust each other at all.