Shadow Web by N.M. Browne

Shadow Web takes you into a parallel universe where Germany has won World War 2.

Jess is just your normal teenage girl living in London, hanging out with her friends. But a chance meeting in Waterloo Station with her double (albiet a double dressed in rather old-fashioned clothes) sees Jess hurled into a weird new/old London.

Different rules apply and danger stalks every conversation and interaction Jess has in this strange world. Who can she trust? Who is on the 'right' side? What happened to the other Jessica? And how is she going to get back home to her mother?

I loved it.

For good readers 12+

http://www.nmbrowne.com/nmbrowne_books.html

Gone by Michael Grant.

Stephen King's The Stand meets William Golding's Lord of the Flies in Gone.

What would happen if everyone over 15 suddenly disappeared from your world? Could you survive on your own? Who would step up to lead? What if something bad happened? Who would fix it? Police it? Make it better again? And what if some of the people began developing weird powers? Powers that could really hurt you and cause some serious damage!

A thrilling, menacing page-turner for the older teen with a sequel 'Hunger' (& at least 2 more books after that) due out later this year. 

A movie is also being made, but get the book with the original cover - it looks far better than the movie-tie edition!