The active topics list only contains topics that aren't locked. Locked topics are not active anymore, so therefore it's not relevant to display them as well.
I'm lost
If you have 'lost' a topic, please go to the right subforum to retrieve your topic, or use the search engine (upper right of your screen) to find locked topics as well.
O ya
Opening a new topic for asking where the old topic has gone is of no use, they will be locked as well.