YA Missing Teenager

I read this book probably about 10-15 years ago now back when I was somewhere in either my teenage years/preteens (I think it was written about then as well) and I'm pretty sure the book cover was pink and the title possibly including the word missing

The book is about a teenage girl who goes missing and the first book involves her friends and classmates being questioned and then the book is them trying to figure out what happened but they don't find out by the end of the book - I don't know if the rest of the books in the series were ever published, I know they weren't at the time that I read the original book

I'm pretty sure it's a US book and was in a high school setting

The other big thing that I remember is that there was an actual website where you could go and there was clues and videos about the 'case'

Some overlap with Cathy's Book. Edit: sorry, wrong touchstone!

>2 beyondthefourthwall: This seems like a really interesting concept! Will give it a read but it's definitely not what I'm looking for

Will let you know if I find any other possibilities!

Was going through some books this afternoon and it occurred to me that there's partial overlap with I Am Princess X by Cherie Priest.