WHERE TO GET VIRAL MARKETING CASE STUDIES?

Reading the site of WOMMA (= Word of Mouth Marketing Association), I have found plenty of 'case studies' and viral marketing examples.
However, the WOMMA terminology is a little bit different. They prefer the term 'Word of Mouth Marketing' instead of 'Viral Marketing'. Because they think 'Word of Mouth' is a broader term than 'Viral'. The last is only a part of the first. The 'Word of Mouth Marketing' comprises, in itself, many types of marketing as, for example, 'Buzz Marketing', 'Community Marketing', 'Grassroots Marketing', 'Viral Marketing' of course, and others. As for me, I can add one more term I have found recently: 'peer-to-peer marketing'.

HOW TO BROADEN TARGET PUBLIC FOR YOUR PR EFFORTS?

This article advises to remember faith-based communities when identifying target public.
Faith-based communities are large, active, and influential. They are well organized and have regular methods of communicating via websites, newsletters, direct mail, and face-to-face interactions. For example, if your restaurant is near a church, make sure your hours and staffing can accommodate parishioners before and after church services, and let the church leaders know you are happy to serve their members. If you are near a Jewish temple, you may want to offer some authentic Jewish and kosher food items.

The PR tip here is to remember faith-based communities when identifying target public for your PR efforts.

PRESENT YOURSELF AS OPEN-MINDED & TOLERANT

In January Pizza Patron (Dallas-based company) began accepting Mexican pesos.
The company's goal was to sell more pizza to its Latino customers. But the company's action attracted public attention. The promotion has been a boon to the company. In January and February sales were up more than 35% compared with the same period last year. The experiment in pesos was to end in February, but then the company extended it through April.
I am not arguing the controversy of using foreign currency in the United States. The very fact of using foreign currency points (in the public judgment) to some broad-mindedness.

So, the PR move for various social, ethnic, racial, national, religious, linguistic, or cultural groups / communities is to present your image to these groups as tolerant & broad-minded.