Beyond that, check out the book "Contagious: Why Things Catch On" by Jonah Berger. I found it very helpful.
"After I sent out that first email, I went rollerblading around a big office park where Tellme was based. I went up to a random guy and said, “Hey man, have you checked out hotornot.com yet?” He said, “No, what’s that?” I said, “Dude, just go check it out!” Then I went home and watched our logs for Tellme and saw a hit come in 10 minutes later, and then more hits kept coming from different people within Tellme.”
-James Hong, cofounder, HOTorNOT
From "Founders at Work"
> “We sent her all over the country,” Munoz told me this week. “Her pitch was pretty genius. She would go to chapters of her sorority, do her presentation, and have all the girls at the meetings install the app. Then she’d go to the corresponding brother fraternity—they’d open the app and see all these cute girls they knew.” Tinder had fewer than 5,000 users before Wolfe made her trip, Munoz says; when she returned, there were some 15,000. “At that point, I thought the avalanche had started,” Munoz says.
http://www.businessweek.com/articles/2014-07-02/tinders-forg... (Paywall)
> Undeterred, Mr. Spiegel and Mr. Murphy shared an updated version for the iPhone with about 20 friends in September 2011. A few weeks in, they started seeing an influx of new users, paired with unusual spikes in activity, peaking between 8 a.m. and 3 p.m.
> It turned out the activity was centered around a high school in Orange County. Mr. Spiegel’s mother had told his cousin, who was a student at the school, about the app, which then spread throughout the school.
> Other high school students in Southern California picked it up, with the number of daily active users climbing from 3,000 to 30,000 in a month in early 2012.
https://www.nytimes.com/2013/02/09/technology/snapchat-a-gro...