If you posted in the thread and have the subscribe function on you an check in your users control panel
for "all subscribed threads" and it will show up there.
In advanced search you can specify the forum and or child forums
to look in, if you know the original thread was in maintenance
for instance. If it was started by someone in particular or you remember someone who posted in it you can search for posts just by that member
You can specify a time frame too in advanced search... last week for instance...
Sometimes it takes some poking around ; -)