The Rise of Nine (Lorien Legacies #3) by Pittacus Lore

Until the day I met John Smith, Number Four, I'd been on the run alone, hiding and fighting to stay alive.

Together, we are much more powerful. But it could only last so long before we had to separate to find the others. . . .

I went to Spain to find Seven, and I found even more, including a tenth member of the Garde who escaped from Lorien alive. Ella is younger than the rest of us, but just as brave. Now we're looking for the others--including John.

But so are they.

They caught Number One in Malaysia.
Number Two in England.
And Number Three in Kenya.
They caught me in New York--but I escaped.
I am Number Six. 
They want to finish what they started.
But they'll have to fight us first