How many members does it take to make a functioning network?

The New York Times reviewed a smartphone app called Sportaneous this weekend. Sportaneous is designed to connect people who want to play pick-up sports games in New York City, but it ran into some challenges. The reviewer wrote,

"The only problem is that the app is not always useful. I tried it repeatedly this summer in hopes of finding a basketball game in Greenwich Village or Astoria, Queens, but never set foot on a court. Internet services like this rely on something called the network effect, meaning that they work well only after they have become popular. With only about 100 people in its system, Sportaneous was stuck at zero."

 In order to deal with the "network effect," the app's creators started promoting the app in specific neighborhoods, hoping to get enough members to support pick-up games. Still, the reviewer said, "People are much more likely to use Sportaneous as a way to supplement and expand the social circles they already belong to than they are to compete against people they have never met."

I thought this was an interesting example of location-based social networking and the challenges involved in trying to get people to move beyond their own strong-tie networks.