Isaiah 41:12

תְּבַקְשֵׁם וְלֹא תִמְצָאֵם אַנְשֵׁי מַצֻּתֶךָ יִהְיוּ כְאַיִן וּכְאֶפֶס אַנְשֵׁי מִלְחַמְתֶּךָ׃

12 You will seek them, but you will not find them—those men who are your adversaries. They will be like nothing, even like nothing at all—those men who war against you.

תְּבַקְשֵׁם וְלֹא תִמְצָאֵם You will seek them, but you will not find them— תְּבַקְשֵׁם a is a piel 2nd sg imperfect from בָּקַשׁ, "to seek." It is naturally followed by the imperfect (qal) תִמְצָאֵם, from מָצָא "find." The waw with the negative is therefore adversative, "but." Note the munach with וְלֹא֣ connecting it directly and inseparably to תִמְצָאֵם. Recall the context of the verse: The "them" refers back to those who "rage against" Israel (41:11). This is picked up by the following phrase"

אַנְשֵׁי מַצֻּתֶךָ those men who are your adversaries. מַצֻּתֶךָ is a derivative of the verb נָצָה "struggle." Here it is in the plural construct (note the Mp "hapax" form note); the plural by itself would be מַצּוּת.

יִהְיוּ כְאַיִן וּכְאֶפֶס They will be like nothing, even like nothing at all— כְאַיִן "like nothing" would have been enough, but the prophet emphasizes his point with וּכְאֶפֶס "like non-existence." אֶפֶס is a reference to the end of the world; what will it be like at the end of the world when God unmakes everything, puts some in hell and the rest in heaven? What will be "left" (אֶפֶס)? Nothing at all. The feeling one gets when you have moved out of a house or an apartment and you look back inside--and there is nothing there. Except, it would be as if the house or building weren't there any longer. This, amplified to all creation, is the point. Israel's enemies will vanish.

אַנְשֵׁי מִלְחַמְתֶּךָ those men who war against you. "Adversaries" is paralleled here by מִלְחַמְתֶּךָ, "those who war against you," a fem construct noun from מִלְחָמָה "war."