A logline tells me what I’m watching for two hours, not just the first act. It needs to tell me what this story is about in an interesting way, a way that makes me want to see how you pull it off. If all you give me is Act One, it sounds like a million other movies I’ve seen.
It also doesn’t tell me what people DO. What do these kids do? Is it simply about escape, as in Dead Snow? Do they try to kill the evil, like in Evil Dead? Is it a mystery to solve, like in Cabin in the Woods? Am I going to watch a teenage slasher movie, or a movie where the kids turn it around on the bad guy? I need to know these things if I’m going to get interested.