Is it possible to post all new threads on a forum to a specific twitter account? 

I looked into site promotion but this seems to be to allow users to login via twitter.

Not what I want : I want the forum to auto - post new threads on twitter.

Promotion is set for a user to manually publish articles to your community’s Twitter account.

I’m afraid, there isn’t anything to automatically publish to Twitter natively.

You may be able to utilize a service like Zapier to do this. 

Zapier FTW!