What's the Name of That Book??? discussion

Hi, trying to remember this book that I read back in school. Can't remember much, but I think I have enough info for someone to name it.

Whodunit camping story
Girl is getting revenge for her friend Michael who was killed DUI from peer pressure
The protagonist turns out to be the killer all along.
Cyanide is involved in the killings, and a flare gun.

That's all I remember =\

Sounds similar to Class Trip. I remember loving it as a kid.

Here's a post about Class Trip. A charater named Michael is mentioned.
http://pointhorror.inthemoonlight.net...

That's the book. Thanks so much!