Transcript for Sunday Spotlight: Reddit Co-Founder Alexis Ohanian

And our "sunday spotlight" today on alexis ohanian. You may not have heard his name before. But if you watched a viral video, there's a good chance it created on his website, reddit. It's taken the web by storm. And it all started in ohanian's dormroom. Abc's rebecca jarvis brings his story. Reporter: Reddit calls itself the internet's front page. Where videos go viral. ♪ This is major tom ♪ Reporter: Where the president will agree to answer anything. All brought to you by the man dubbed the mayor of the internet, alexis ohanian, who with co-founder steve huffman, started the website eight years ago, while students at the university of virginia. Reddit is a platform for online communities to share links and have discussions. Reporter: Does it look like you envisioned it years ago. I wanted to make something that worked. It was me and steve in a little apartment, with laptops, who were told by lots of important people that we were rounding errors. And you know what? We ate it up. We ate it for breakfast. It was motivation. Reporter: Motivation that sparked an internet sensation. REDDIT'S SIGNATURE IS THE AMAs, Or ask me anything session, attracting stars like tom hanks, bryan cranston. Thanks for welcoming me to reddit. Reporter: And seth rogen. Who would you like to see do one? I would love to get jay z. Reporter: And reddit recently broke through the 80 million user mark, giving users power to turn a link or video viral in seconds, just by voting it to the site's front page. What's the secret to getting there? The secret is good content. At the end of the day, it's having great content. Reporter: But reddit has come under fire for allowing users to post illicittos. And after the boston marathon bombing, several combed through online video to search for a sut and identified the wrong person. Who isponsible for that? Those people. I think -- Reporter: You don't think that the companies that create the forums for those people, are responsible? We always have to hold the people accountable, not the platforms themselves. This is a problem humans, ght? Journalists, theest trained, smart people in the world, have made the same mistakes before. I'm happy with reddit's stance in coming out and apologizing for it. Reporter: Ohanian has sold his stake in reddit. But he continues on the company's board. And he also invests in and advises more than 50 start-ups. His new memoir, part autobiography, part how-to guide for those looking to join him in the internet boom. What do you think is the biggest mistake of people trying to stcompanies today are making? They get caught up with the idea. It's sort of called launcherpreneurship. It's all a remix. And everyone has great ideas. And what matters is execution. So, so many people who decide, all right, I'm going to start this thing, never get to building something and presenting it to users. Reporter: You said this is just the tip of the iceberg, though, in terms of the internet? So, what does the future look like? I wish I knew. There are people right now all over who are just a away from actually getting started on the next great thing. And I really want them to because I want better stuff. Reporter: For "this week," rebecca jarvis, abc news, new york. Thanks to rebecca for that. And you can read an excerpt of alexis ohanian's new book. "Without their permission," on our webse, abcnews.Com/thisweek. Now, to newsrom afghanistan. And the pentagon did not announce any dths of service members in afghanistan this week. That's all for us. Thanks for sharing part of your sunday with us. Check out "world news" with david muir tonight. And I'll see you tomorrow on "gma." Time to go on the record.

This transcript has been automatically generated and may not be 100% accurate.