YA novels The Mortal Instruments series

City of Bones and City of Ashes. Book 1 and 2 in the Mortal Instruments series. Series description: Clary Fray's search for her missing mother leads her into an alternate New York called Downworld, filled with mysterious faeries, hard-partying warlocks, not-what-they-seem vampires, an army of werewolves, and the demons who want to destroy it all.