Social media has emerged as a leading source of news among online users who increasingly access it on their smartphones, a thinktank said yesterday, warning that the embrace of free news was becoming a challenge for publishers of quality news.More than half of online users get their news from Facebook and other social media platforms, refusing to pay for news and using ad-blocking, which hurts publishers' revenue, the Reuters Institute for the Study of Journalism (RISJ) said. But although free news distributed through social platforms creates an opportunity to reach more readers, it also makes it more difficult for publishers to get recognised and connect with their audience, the RISJ said in its annual Digital News Report."These things are happening because of us," Rasmus Kleis Nielsen, Reuters Institute director of research, told the Thomson Reuters Foundation in a phone interview. "We prefer news in the digital form because it's convenient but you get what you pay for. It takes money to do professional journalism."