From Four Numbers That Explain Why Facebook Acquired WhatsApp by Jim Goetz:
From the moment they opened the doors of WhatsApp, Jan and Brian wanted a different kind of company. While others sought attention, Jan and Brian shunned the spotlight, refusing even to hang a sign outside the WhatsApp offices in Mountain View.
…There may be no greater testament to the viral nature of WhatsApp than the fact that the company has accomplished all this without investing a penny in marketing. Unlike their smaller competitors, it hasn’t spent anything on user acquisition. The company doesn’t even employ a marketer or PR person. Yet like the world’s greatest brands, it’s created a strong emotional connection with consumers. All of WhatsApp’s growth has come from happy customers encouraging their friends to try the service.