You search high and low for what you want.

你到处寻找你想要的东西。

I've been searching high and low for them.

我一直在到处找他们。

I've searched high and low for my car keys and I can't find them.

我到处找我的汽车钥匙，就是找不到。

The public were profoundly concerned; they searched high and low, they dragged the river for his body.

公众深感关切；他们上上下下寻找，他们拖河寻找他的尸体。