In the traditional publishing world, word count for young adult novels is all over the place. The Twilight Saga books are each over 100,000 words. Books like Kate Brian's Private series are more around the 65,000-75,000 word count. Most websites and agents place a typical YA manuscript between 45,000-80,000 words. Here is what Agent Colleen Lindsay says about YA:
YA fiction = For mainstream YA, anywhere from about 45k to 80k; paranormal YA or YA fantasy can occasionally run as high as 120k but editors would prefer to see them stay below 100k. The second or third in a particularly bestselling series can go even higher. But it shouldn't be word count for the sake of word count.