VBulletin supports a function called Member List - which basically does what you want, i.e. find a member.
However going through the link in the FAQ produces this:
Sorry! The administrator has disabled the list of members.
- it appears that the function has been disabled in PPRuNe.
Unless one happens to be a moderator or administrator - we have the facility in the Mod CP.
do a search and then plough through threads looking for one of their posts.
It would be quicker to Show Results as posts, not threads in your search - see the check box in the advanced search page. That should bring you straight to their posts - in fact you can go straight to their profile from the search results page.
SD