From the FAQ
Why did my thread disappear?
There are several reasons why a thread you posted no longer appears where you posted it. If another thread already exists on the same topic, the staff will usually merge the threads to keep all of the conversations on that topic in one place for everyone to read. This may also occur if the staff moved your thread to a more appropriate forum. Of course it is possible that the thread violated the Forum Rules or the staff felt the topic or content of the thread was not appropriate for the site.
For more questions and answers, read the FAQ
You can access it at any time by clicking the FAQ link below the site logo.