Like a player in one of the games now offered on his site, entrepreneur Justin Kan has discovered a second life.

Kan gained Internet fame in 2006 when he launched Justin.tv and broadcast the details of his daily life around the world. Five years later, with 30 million people a month using the site to watch and stream video of their own, Kan decided to shift his 45-person team's attention to the next big thing.

The result is TwitchTV, a rapidly growing site that lets users broadcast themselves playing video games to a global audience. Since launching in June, the site has attracted 12 million regular viewers. The number is growing by 11 percent a month.

The site's popularity can be attributed to a surge of interest in gaming, the increasing number of adults who grew up playing video games, and a wider variety of places with game content online.

"Everything has hit this inflection point, which points to there being this thriving and vibrant ecosystem that's growing up around it - of which we're just a part," said Kan, 28.

Surge in spending

Consumers spent almost $54 billion on video games last year, up from $33 billion five years ago, according to a PricewaterhouseCoopers report. The report predicted that video games will be the fastest-growing category in entertainment, with estimated 2015 sales of $79 billion.

The seeds for TwitchTV were planted last year in Justin.tv's San Francisco offices, when Kan and his co-founders noticed a small but dedicated group of gamers spending increasing amounts of time on Justin.tv watching one another play video games. Emmett Shear, the company's chief technical officer, assigned two engineers to try to attract more gamers. The more features they built to help gamers, the faster the site grew.

In June, the company spun out Twitch.tv, a stand-alone site where players and spectators can interact. Within two months, the site had 8 million unique visitors and is on pace to double that number in less than a year.

The company has also signed revenue-sharing agreements with 1,000 popular gamers and media companies, who earn a share of the money TwitchTV makes by showing advertisements before and during the games.

Playing games for a job

The site is popular with people who earn a living playing games, and can now make money simply by practicing for tournaments and streaming it to their fans. Top gamers are earning $5,000 to $8,000 a month streaming their game play online, said Marcus "djWHEAT" Graham, a game commentator and broadcaster.

"The biggest catalyst for success has been live video streaming," said Graham, who recently joined TwitchTV in a move to attract prominent gamers and competitions to the site. "Not only did it enable top-level players to showcase their own play outside of tournaments, but it allowed an entirely new audience to have easy access to watch these pros and learn from them."

The biggest site for watching games remains YouTube, with more than 11 million game play videos. Searches for gaming have risen 38,000 percent since February 2008, a spokesman said. YouTube has also proved lucrative for those with whom it has revenue-sharing deals.

OnLive, a cloud gaming service that streams game play to desktops and mobile devices, last year introduced a feature that lets people watch others. It has become one of the site's most popular elements, said Steve Perlman, the Palo Alto, Calif., company's founder and CEO.

While playing Assassin's Creed: Brotherhood recently on his service, Perlman became stumped about what to do next. After he stumbled around 15th-century Rome for a while, a spectator sent him a message with a hint on how to proceed.

"It saved me going and getting frustrated for two hours," Perlman said with a laugh. "It was great."

cnewton@sfchronicle.com.