On any given day, Jayson Love fires up a personal computer from his Billings, Mont., home and starts his job—playing videogames in front of an audience of thousands.

The 33-year-old hosts a Web show called "MANvsGAME," in which he broadcasts his live gameplay on the site Twitch. Between advertising and subscribers paying $5 per month to watch his video stream, he says it is possible he'll earn more than $100,000 next year.

Mr. Love is part of a growing group of gamers whose antics are turning videogames into an online spectator sport. Most say they stream their gameplay to connect with other people, and those who earn money usually make just enough to feed their hobby.

Their efforts have helped Twitch become a social center of the videogame world. The two-year-old website sends streams from more than 600,000 broadcasters each month to some 45 million gamers.

The trend could soon kick into a higher gear.