You want to know the guy who realized the market entry of Facebook in the German speaking market: its Adrian Locher. With his agency SMABOO, he created a word of mouth effects through his ambassador marketing strategy for German facebook.
He especially recommends that strategies for companies with already strong brands, cause he will activate already existing clients or users and turn them into active ambassadors for the products of even the whole company.
If you as a startup want to create such effects you should find your best and your heavy users and get in contact with them. "Make them part of your marketing strategy".
Started in Switzerland, Adrians agency soon moved to Berlin, cause of it's huge creativity, availability of human resources and the cheapness of resources.
Check out more interviews realized at the great LIFT conference Geneva, Switzerland in February this year.