I've been following the general topic of Growth Hacking for a few months, both here and on Quora. During this time, I've learned about the value of viral loops and referral programs. It seems to me that most techniques are focused on products (apps), and not services (such as a User Experience audit). I was hoping that someone could point all of us service based companies to some of their favorite resources, case studies, articles, videos, etc that discuss successful viral loops and referral programs! For a bit of background, my partner and I run a User Experience Agency (http://gobysavvy.com/) that focuses on a somewhat "productized service", a User Experience Review, as well as more in-depth design services. We've set up tons of marketing funnels from ads and social media, through email, through actual sales outreach. However, this takes a lot of manpower and a personal touch. Is there another way, utilizing principles of growth hacking? More specifically, utilizing viral loops and/or a referral program?