Beyond customers and professional colleagues, friends can be a valuable source of information and potential business opportunities.

When it comes to business and career advancement, we often discount one of our greatest resources: our friends. Our friends and peers may know our general profession, but they rarely know the specifics of what we do. They don’t need to shadow you on the job, but your social network should at least know who you serve, how you serve and how well you serve…

http://www.forbes.com/sites/theyec/2012/07/18/dont-discount-your-best-business-marketing-weapon-your-friends/