Just wanted to make sure that if I close my forum - all the content and messages will delete and not be searchable to random people online?  Is that true?

I joined delphi plus to try to make all my folders private, but it doesn't seem to be working. 

While you can close a forum to remove its contents from any further access on Delphi Forums, it does not mean that search engines do not still have records of what was there in their indexes. Or the Wayback Machine at archive.org may, also. Once something is posted on the Internet, it may be accessible forever. There is little you can do about it.

They would have to know what to search for and stuff right?

If you delete your profile, do your messages in forums delete as well?

I can't answer your first question. There are too many variables.

Closing your account does not delete messages.