Planned publicity that spreads spontaneously and rapidly 'by word of mouth' (but also by social network sites) throughout a potential media consumer market, refers to:

Planned publicity that spreads spontaneously and fast by word of mouth and social networks across a consumer market is viral advertising.

The term borrows the idea of a virus, spreading from person to person without paid placement at each step.

News means factual reporting of current events, not a planned self-spreading promotion.

A communique means an official statement issued by an authority, a formal announcement rather than organic buzz.

A rejoinder means a reply or counter-response, having nothing to do with promotional spread.

Its defining trait is self-propagating word-of-mouth momentum built by design.