Especially when it comes to social and shopping, women rule the Internet.

Female users are the unsung heroines behind the most engaging, fastest growing, and most valuable consumer Internet and e-commerce companies.

If you're a digital startup, building and highlighting your social proof is the best way for new users to learn about you.

What is social proof? Put simply, it's the positive influence created when someone finds out that others are doing something. It's also known as informational social influence.

If you're looking to grow your user base, is there a best way to cost-effectively attract valuable users? I'm increasingly convinced the best way is by harnessing a concept called social proof, a relatively untapped gold mine in the age of the social web.

Consider the social proof of a line of people standing behind a velvet rope, waiting to get into a club. The line makes most people walking by want to find out what's worth the wait. The digital equivalent of the velvet rope helped build viral growth for initially invite-only launches like Gmail, Gilt Groupe, Spotify, and Turntable.fm.