Marked question

When I was in High School I remember reading a really good Supernatural Series. I have never been able to remember the name and it was from the school library. It would have been form 2006 to 2009 as I graduated in 2010 and had already finished by then. I believe there was at least 4 books that I read. I remember there being a "secret world" that humans could not see but only 1 person could. I would appreciate it if you would comment any type of book that relates to this and maybe I will remember.

NOTE: It is not about Marked. I have never read this book as far as I know but it does not sound familiar.