what happend to search in thunderbird

It's still there. For the toolbar at top, rightclick, select customize, locate the search icon and drag to bar. the search feature is also at Edit>Find from the menu bar.

I must be blind but I cannot find it.

Just a suggestion: drag another icon to the toolbar to see if it displays there. I am wondering if the text for toolbar is black with a black background. I state that because all icons appear where your screenshot is unless they are already active.