The forums have a specific cut-off date for displaying threads. I think it's just a month. In Poetry, there's not a lot of posts to keep threads active, so many of them fall off the display page.
In the lower left corner of the bottom of the forum, there should be drop-down menus for displaying threads. So, for instance, if you go to Poetry, scroll down to below the New Thread button, you'll see the three drop-down menus. Click the one at the end, and set your display date (from last day to the beginning of PC's existence). If you click on the option to display threads from last year, and go to page five, then you'll see your other poems.
I hope that helps you out a bit. I'm kind of tired from work, but I didn't want to leave you waiting for an answer. Your poems are still around, but aren't able to be seen unless the forum settings are changed.