The WhereIs command (W) is available in many of Pine's screens. It searches through the contents of whatever is on (but not ``behind'') the screen you are looking at: the current message, the current folder index, the address book, and so on.
WhereIs also lets you quickly jump to the first (<Ctrl>Y) or last (<Ctrl>V) of the items on the screen you are searching: the first/last message in the FOLDER INDEX, the first/last address in your ADDRESS BOOK, the first/last line in your COMPOSE MESSAGE screen, and so on.