3 ways:
Mods who move things generally add comments to say what has happened. There's at least one trust level 3 member who often moves posts and he too adds comments to say what he's done. Adding a comment generates a notification, which the OP should see and thus bring them to the topic.
As soon as someone else replies then that will generate a notification, leading the OP back to their topic.
If someone really can't find a topic they have created then they look in their profile under summary where they can see there is a list of Top Replies and Top Topics, they should be able to find their topic in there.