The Raft by S.A. Bodeen

 Robie lives on a remote island just off the mainland of Hawaii, but far enough to make life uninteresting.  To socialize and get a taste of culture, Robie often goes there by supply plane to visit her aunt.  Her current visit is cut short when her aunt needs to suddenly leave town.  Robie begs to stay alone, and for once, her aunt agrees.  It's only for a week and even though Robie has never stayed alone overnight, she is has been responsible in the past.  Robie heads out one day from her aunt's apartment and has a freaky encounter with someone that leaves her totally shaken. This leads Robie to head back to the supply plane and home.  But she never makes it home, as the supply plane crashes in the ocean and only she and the co-pilot survive.  Her biggest challenges are yet to come.  No one knows where Robie is, and time is running out.
If you are a fan of survival books, you will love The Raft.  It is a quick read, with some predictable moments, but one that you won't put down until you find out what happens to Robie.