The Hidden Oracle by Rick Riordan (The Trials Of Apollo #1)

Apollo, the once glorious god of the sun, music, poetry, and more, has been cast down to Earth in punishment by Zeus. Now he is an awkward mortal teenager named Lester Papadopoulos. In order to regain his place on Mount Olympus, Lester must restore five Oracles that have gone dark. But how is he supposed to accomplish this task without having any godly powers? It's time to recruit some help. A certain demigod named Percy Jackson shows him where he needs to go: a training camp on Long Island called Camp Half-Blood.