This could happen for a number of reasons.
Perhaps it was posted in the wrong place and a Mod or Admin has simply moved it to another board within the same forum.
If you've looked at all the boards in that same forum and still not found your posting, it could be that the Mod or Admin has deleted it by mistake when trying to move it. This does happen from time to time, though of course we try to avoid that kind of thing.
It could also be that the topic is now out of date and has been removed as part of a general clean-up. Every so often we do this to try to reduce the load on our server and to keep the fora running as smoothly as possible.
But most likely the posting or thread breached our guidelines and the Mod or Admin thought it was too much bother to edit - it's so much easier just to hit the delete button.
Postings which breach our guidelines may be edited, locked or deleted without explanation. So please make sure you've read the guidelines.