The new forums removed the individual Forum Search in favor of a universal CNET search.
However, if you search for your term you can still narrow down your search using the filters in the left column of the search page, and there is also an option at the top of the page to show the "Most recent" results, instead of "Most relevance".
I hope that helps.
I have looked everywhere but cannot find a "search" function for just the forums.
After I have logged in and found the topic that I want to search under, there is no "Search" to be located.
There is the BIG search box at the top of the screen, above the Home/etc buttons, but that allows me to search either the ENTIRE Cnet site or the internet. I want neither of those, I just want to search the forum topic I have selected.