u/CutieShadows

Read it back in my highschool library (roughly 10 years ago) all I remember was it having a green cover, may have been part of a series, it already looked kinda old, it was horror fiction and there was a monster who kinda reminded me of Slenderman. I think a girl in high school was the main character set in modern day. I could be wrong but I think a scene in the book was monsters using a portal to get to a bunch of kids and killing them.