Dark fantasy middle school/ya novel from late 90s about girl who goes into forest to find brother who was lured in there by mysterious/sinister teenage boy. Other creepy children also live in the forest and heroine encounters many supernatural things on her journey to find her brother. Book cover had screaming face stuck in a wall.
Stump the Bookseller
New format, same book stumper solving.
I should probably elaborate a little more! Brother and sister visiting their aunt (bea?) and meet a teenage boy at the edge of a forest who tries to talk them into following him. Sister stops them but later on her little brother goes in there and she goes in to find him. I remember she encounters an evil little girl sitting in a tree and some kind of weird blob thing that makes her want to fall asleep. She meets the teenage boy again who she has a creepy kind of chemistry with and it turns out he got lost in the forest years ago himself and actually knew the girl’s mother when she was a girl.
Maybe The Stranger by Caoline B. Cooney? An old Point Horror cover matches your description; the plot has some similarities.