I read back in the late-2000s. I doubt they would have been written before 2000, but I could be wrong. I don’t remember too much about these books besides the female narrator and some… weird concepts. It surrounded a town where monsters came out after dark (or something like that), and a group of teens would fight them with enchanted weapons. There was a whole premise of certain numbers holding great importance. I think they would enchant their weapons by labeling them with 13-letter words. That might not have been it exactly, but I do remember a huge thing being the 13-letter words. Pretty sure there was a love triangle, too (but who’s surprised!).
Lost Classics of Teen Lit: Name That Book! 