In the upper right corner of your screen, you'll see your login name and the sign out button. Just below that is a search bar.
See where is says "this topic"? You can click on that gray box and get a drop down menu - you can search "this forum" "blogs" and other options. You can also click on the magnifying glass and be brought to more advanced search options.
Alternatively, you can go to google and type your "search words + ACN" or "search words + latitudes" and find older conversations that way. I do both. If I'm looking for a post by a certain member, or I want to use a date range, I use the forum search tools. If what I'm looking for is a few years old and is more vague, i use google.