everywhere多用于肯定的情况,而anywhere多用于疑问和否定.前半句陈述一个肯定的事实所以用everywhere.
如果后半句是he couldn't find it 这里可以加anywhere.对比的来看的话,这个句子可以写成Tom looked for his bike everywhere but he couldn't find it anywhere.这样就比较好理解了.