Many news outlets are struggling to profit from smartphone content as more people discover news through search engines and social media rather than the front page of a news website, said the Reuters Institute for the Study of Journalism.

Online advertising revenues are falling as smartphone users, who spend half of the time on their devices reading news, become increasingly frustrated by advertisements and so-called sponsored content, the RISJ said in its annual Digital News Report.

"Most people like news and use news, but they don't want to pay for it, don't want to see advertising around it, and don't want to see it mixed up with sponsored content," said RISJ Director of Research Rasmus Kleis Nielsen.

"This means sustainable business models remain elusive even for those who succeed in building an audience," Nielsen said in a statement as the report was released.

Only the most loyal smartphone users are using news apps, as others rely on social media, messaging apps, email and mobile notifications to read online news, the RISJ said.

While more than two-thirds of smartphone users have downloaded news apps, only one-third use them on a weekly basis.

Four in 10 smartphone customers use Facebook to find, read, watch, share and comment on the news each week - more than twice the usage of its nearest rival, Youtube, and almost four times that of Twitter, the RISJ said.

Newer networks such as WhatsApp, Instagram, and Snapchat also showed the growing importance of social platforms worldwide, the report said.

Although most smartphone users praised social media for bringing them stories they would not have seen otherwise, they said they had reservations about the accuracy and reliability of news found in this manner, RISJ said.