I've been investigating the forum search function.
First, if you type a search term (or multiple terms separated by commas) in the "search" window box in the upper right corner of the forum page just below your name, you will get a multi-page list of every post satisfying your search term(s) from all forums. I believe, unlike the previous search software, it will search the title as well as the body for the search term.
At that point you can click on the down arrow at the end of the new search term line and you will be shown and expanded search page where you can refine your search- select an area, tour, etc.
Now it is also possible to search for a post by an individual user (Author.) You don't need to guess, just start typing the user name and you will be shown all close matches. By adding an "Author" you limit results to posts by that person, e.g. my test search for "balloon" in "Africa" and subcategories yielded 8 pages of results. When I put "AlanS" in the "Author" line I got only two pages of results, each page had multiple threads containing a post by AlanS that mentioned "balloon."
You can select a specific tour, but you may miss relevant posts in a related tour. So, unless you are certain which forum the topic was discussed or answer posted, I recommend selecting the highest category by region, e.g. Africa instead of K&T and then checking "search subcategories." I couldn't discern the impact of checking "search archived." In my test I saw results from back in 2011. That is old enough to be of limited use.
Anyway, the search function is still a very useful tool.