You can do that by yourself easily. Press "All" instead of viewing each page one by one (or add ";all" to the end of any thread link), and then CTRL+F. Type in whoever you're suspicious about and presto!
This only works if the thread is (equal to, or) shorter than 25 pages on this forum. Therefore, this won't work in bigger threads. Additionally, it would be better if a separate page opened with the desired results (so that one does not have to open a single page with thousands of replies). On longer threads I use "print" instead. It includes quotes though.
Another way would be to do a search for posts by the user in question, use (part of) the threads topic as search criteria and check "Search in topic subjects only".
