If you notice that your post is missing, it could be from three things.

Merged: Post will be merge is there is another one already created.

Moved: If you post in the wrong category, your post will be moved to the appropriate category. Please make sure when posting you are posting in a category that relates to your post, otherwise it is considered spam and could get your posting privileges taken away after many occurrences.
If your post was moved, you can go into your profile and view your recent posts and topics OR you can do a forum search.

Deleted: If your post is just not fit for the forum, then it will be deleted.