In the past two weeks two people I know have had difficulty trying to find a link or information from an old Facebook post. It seems that Facebook just can't do search.
Here's a work around:
Select "Account Settings" (down arrow at far top-right of screen). At the bottom of the account settings screen there is a "Download a copy of your Facebook data" link. Click on that and follow the procedure. It takes several hours for Facebook to generate an archive of all your data. Once complete you will be notified by email and a link will be provided where you can download a ZIP archive with all your stuff.
Unpack that ZIP and use your browser to navigate to the unpacked directory. Look for file "wall.html" in directory 'html'. That's a HTML page with all your posts.
Now use the browser's in-page search (usually CTRL-F or use the browser menu) to search for what you're looking for. The browser in-page search is a simple substring search... but hey... it's waaay better than what Facebook can manage.