We rushed out of the store, but the thief had vanished into thin air.

vanished 是动词 vanish 的过去式，vanish 的意思是"消失、突然不见"，常用来形容人或物突然从视线中消失。vanished into thin air 是一个固定表达，字面意思是"消失在稀薄的空气中"，实际表示"完全消失不见"。