Give "them" something to talk about. That is the main idea for any public relations and social media campaign. People need something, anything really, to talk about. Molly Cyrus went whole hog with the over-the-top stage performance (an old Hollywood shock trick) and Coca-Cola went simple. It's such a small idea, put inviting words on cans of soda and create a "share a coke" campaign. You have the cans. You print on the cans anyways. This simple concept has created a lot of buzz on an old brand (yes, it's a strong brand) and an old product (yes, a dominant product). Simplicity is usually another key to social campaign success.
Coke didn't need a multi-million dollar TV ad budget to set the conversation wheels in motion. Everyone was talking about the cans at my last family barbeque. Simple and effective. Everyone, no matter what their business, needs to give people something to talk about. The more personal, shocking or unusual makes for the largest impact. If you combine that with a developed network of communication like your email lists, Facebook followings, etc. then you have cheap tools for an impromptu promotion.
If you combine it with a call to action - YouTube video, trial offer, new product launch, etc. then you have the vehicle to monetize the effort.
For Public Relations ideas try this article "Public Relations, A Secret Weapon DIY".