Thou shalt seek them - This denotes that it would be impossible to find them, for they should cease to exist. The whole verse, with the verse following, is emphatic, repeating in varied terms what was said before, and meaning that their foes should be entirely destroyed.
Related Commentaries of Isaiah 41:12
Isaiah 41:12
12 Thou shalt seek them, and shalt not find them, even them that contended with thee: they that war against thee shall be as nothing, and as a thing of nought.