Hi there, thanks for using Wonder to ask such an interesting question.
Unfortunately, I wasn't able to find a lot of concrete numbers about the market size of livestreaming. I found one study about the livestreaming market stuck behind a paywall, and some general statistics about streaming in general and livestreaming sports and gaming.
What numbers I could find do indicate is that it's growing. One study reported 214% growth in live video ad views year-over-year. Most popular is livestreaming is of sports -- about 38% of Americans who watch sports online do so through livestreaming. The biggest livestreamer of sports is MLB Advanced Media, the media branch of Major League Baseball. Others use livestreaming for playing video games or watching movies, listening to music, recording events including concerts and religious services, making art, cooking, and just to narrate their daily life.
While the new mobile livestreaming apps Periscope and Meerkat have been heralded as game changing, they haven't nearly risen in popularity the way Twitch.tv has -- market penetration is low, with only 20% of Internet users or so claiming to have given these mobile apps a try. However, on August 10, Periscope announced it had 10M active users. All I could find for Meerkat was that it had 2M users as of May, and we can assume that number has grown somewhat. That Meerkat didn't fire back at Periscope with their own user numbers after Periscope's disclosure has been widely interpreted to mean they have fewer users. As these services are still very new, we may expect their usage numbers to continue to change as the year progresses. Also, Facebook has just entered the market as a competitor to Periscope and Meerkat, leveraging their huge user base (Twitter, which owns Periscope, has 304M monthly active users, compared with Facebook's 1.49B). At current, the livestreaming functionality is only available to celebrities, but it is being rolled out to all Verified Facebook Accounts by the end of the year, and eventually is expected to become a feature available to all Facebook users.
For people producing livestreaming content outside of major corporations, ad revenue seems to be the major source of profit. For the companies themselves, that's actually information they seem to be guarding pretty heavily -- but for the leaders of the field I did some digging trying to find their total number of users and any revenue information they had out there. I found some revenue numbers for 2013 to give you an idea how much money livestreaming companies are making, but they don't like to share how many subscribers they have or what their grip on the market share is.
The top name-recognized livestreaming services seem to be:
Periscope (>10M users)
Meerkat (at least 2M users)
While there are other, older services, like Vokle and Youtube livestreaming, they haven't made nearly as much money or received as much hype as these five.
Thanks for searching Wonder! Sorry I couldn't get you more precise numbers about the market share, but hopefully there's some useful information for you included in the links below anyway. Please ask another question if you're wondering more about livestreaming or anything else.