Sometimes Cipsoft has forum maintenance or clean up. There was a cleanup dated December 2009 where the news stated, "Tomorrow afternoon, we will perform a forum clean up. This means that all threads in which the last post is older than two months will be deleted." The oldest threads you can find have the last reply dated "01.10.2009". Any thread before this last reply date was permanently deleted, so please note some threads could be gone forever. Source: https://www.tibia.com/news/?subtopic=newsarchive&id=1165&fbegind=28&fbeginm=2&fbeginy=2006&fendd=29&fendm=3&fendy=2020&flist=11111111
There's a search option on the forums but to get to it you need to go to Tibia's website, click on forum on the side, click any forum, for example, I went to world boards, then I clicked Antica, now you should the main page but you can scroll all the way to the bottom and you'll see where it says board jump, thread jump, post jump, and page jump. (ex. 1) You can't search by words.
If you don't know what numbers to put then you'll have to search for the thread manually. To do this scroll to the top of the page where it says show thread from you want to click on the down arrow and select all threads (ex. 2). Now you need to swift through the pages to try to find the thread you're looking for. What I like to do is take notice of the dates listed to give you a rough idea as to what page the thread might be on. You can take advantage of the page jump and just rough estimate what page the thread could be on (ex. 1). Once you find your thread I would take note of the post number (listed in red on ex. 3) and the thread number (listed in orange in ex. 3). I would also recommend bookmarking the thread that you want to keep if you want to avoid going through the hoops of searching for it later.