The Lorien Legacies are a series of books written under the pseudonym of Pittacus Lore, the elder entrusted with the histories of the Nine.
Nine alien youngsters are hiding out on Earth, the last of their kind, each of them unaware of the others and protected by an alien Guardian. These nine have to move about constantly to avoid detection as they are hiding out from another alien race who would wish to kill them. The nine have a protective charm however, they can only be killed in a certain order - which seems like an odd charm, why not just make it so they can't be killed - starting with number 1 and working through to number 9.
So far, the first three have already been killed. Now number four must go on the run as the alien killers appear to have found him.
It's a YA book and has some clumsy relationship scenes, but that's not really what the story is about. Looking forward to the next book...