FORTUNE — Charlie Todd did the starving actor thing when he first moved to New York at 22 in 2001. On the side, he and his buddies staged pranks in public spaces, trying to make people laugh.
Over a decade later, those public performances — and the organization that he built to pull them off — have become Todd’s main source of income. His group, Improv Everywhere, is a long-form improvisation troupe that organizes events like the annual “No Pants Subway Ride” in New York, and other great feats of public absurdity. In 2008, for example, Improv Everywhere coordinated 200 people to freeze in place, at the same time, for five minutes in Grand Central Station.
Todd has written a book called Causing a Scene, published in 2009. Now he speaks at colleges and universities and even consults other organizations about what makes a successful viral phenomenon. He took some time to explain to Fortune how an unknown aspiring actor gained the power to get 4,000 people to simultaneously take off their pants.
How do you get so many people to agree to do one thing at the same time?
I’ve developed those skills over the last 11 years. The projects I do are open to everyone, so I have to design them in a way that anyone can participate. In the No Pants Subway Ride, for example, the two requirements to participate are the willingness to take off your pants in public and the ability to keep a straight face about it.
And lots of people can do that?
About 4,000 this past year.
Yeah, you know, when I first started Improv Everywhere, the people who participated in it with me were actors or comedians. It didn’t occur to me that someone who was, say, a lawyer would want to do this.
A lot of people who participate in Improv Everywhere events see it as a confidence builder — as sort of a personal challenge to try something new and stretch themselves. That was really never my perspective. I was a performer already, so to me, it’s really no big deal to take my pants off on a subway car if it’s being done for a reason.
Do you think it helps the group’s appeal that the events aren’t mean-spirited like other pranks?
That has always been the goal. I really believe in the golden rule of the prank: any prank should be as much fun for the person getting pranked.
Every organization faces quality control issues. How do you grow as a group but still maintain the integrity of an Improv Everywhere performance?
There have been some challenges as we’ve grown. It’s just not practical to always do things with thousands of people. I have to sort of evaluate every idea and consider if it should be open to everyone or would be better served with fewer people.
It’s been important for our longevity to constantly come up with new ideas. As long as it feels fresh every time we do a new project, we’ll remain relevant.
What can companies looking to up their social media game learn from what you do?
Brands are turning to web video and social media and realizing that’s where the audience is. The main advice I have for people trying to make content online in conjunction to a brand is to not make commercials, but instead to realize how important it is to create really exciting content first. There have been examples of brands sponsoring someone who’s already doing something awesome who can then do something even cooler with a brand attached.
But Improv Everywhere has remained brand-less, yes?
I think a big appeal of our projects is that there is no agenda behind them — it’s comedy for comedy’s sake. People approach me a lot about doing things that would have a message and be more activist-based. I think the tools I use with Improv Everywhere are tools that activists could certainly use to great effect. But if you have 200 people freeze in place, that seems like magic. If you have people freeze in place with t-shirts that say “U.S.out of Afghanistan Now,” it’s a clever protest, but people say, “Oh, I know what that is, it’s a protest.” It doesn’t feel as much like magic.
What has Improv Everywhere taught you about leadership?
How important it is to maintain the trust that you have with those you’re leading. Over the years … I’ve realized that 95% of the people who show up I don’t know personally. Still, they’re trusting it’s going to be fun, well thought-out, and organized. This means that I can have a few thousand people pretty much do whatever is asked of them. If I were to ever do that in a way that’s exploitative or not a good use of their time, it would be my last because it would break that trust.