Freenet's keyword search functionality depends on (anonymous) maintainers of search indexes, running crawlers and indexing the content they encounter. Crawling Freenet is hard work and can be legally challenging. As far as I know, there are no currently maintained search indexes.
By design, Freenet only retains content while it is new, or while it remains popular. The known indexes are outdated, so they are neither new nor popular. This caused them to have disappear from the network almost entirely, which you seem to have experienced first-hand.
Lacking a functional search, there are still other ways to get around Freenet. The default set of bookmarks includes a handful of index sites, such as Enzo's Index, that to some end provide an overview of websites available on Freenet. Also note that there's quite an active community on FMS and Sone, which are Freenet's forum and Twitter equivalents, respectively. You can find more about both in the Freenet Social Networking Guide, which is also included in the default bookmarks.