I Am Number Four by Pittacus Lore

I Am Number Four by Pittacus Lore (a pseudonym for James Frey and Jobie Hughes) and the first book in the Lorien Legacies series. The book I Am Number Four was published on August 3, 2010, and spent seven straight weeks at #1 on the children's chapter of The New York Times Best Seller list. DreamWorks Pictures bought the I Am Number Four rights to the film in June 2009; the movie I Am Number Four was released on February 18, 2011
The novel I Am Number Four is the first of a proposed six-book series and follows the story of John Smith, a 15-year old alien from the planet Lorien, and Henri, his guardian Cêpan, as they run from the Mogadorians, another alien race that is hunting John and eight other teenage Lorics residing on the planet Earth. These nine teens are members of the Garde, a group of Loric people gifted with special powers called "Legacies." Cêpans, who are also Loric, do not acquire legacies and most often become protectors and mentors for young members of the Garde. The teenagers are protected by a spell or charm that only allows them to be killed in numeric order. The first three have been killed, and John is Number Four.
The book I Am Number Four opens with the death of Number Three. Number Four is introduced under the alias Daniel Jones as he leaves Florida. Four has three circular scars which begin on his right outer leg, just above his ankle, and move upward along his outer calf. Each signifies the deaths of Numbers One, Two, and Three, and burn with blue fire when they appear... (Summary by Wikipedia)