Twitter wants more of that kind of user engagement. It recently rolled out a targeted notifications feature for emergency alerts and crises, and it now hosts an experiment account called "Event Parrot" for delivering breaking news via direct message.
A recent Pew survey indicated that about half of both Facebook and Twitter users in the U.S. get some of their news on those sites.
The latest moves reveal a new level of ambition to deliver the news, and if they provide the right mix of content, the sites eventually could succeed in becoming places where people get most of their news.
"If Facebook can surface enough content, with enough variety, they might convince me I can get everything from them," said Gilbert of the Medill School of Journalism.
Facebook's interest in news could be related to the fact that people are starting to show signs of fatigue with its platform, said Joshua Benton, director of the Nieman Journalism Lab at Harvard University. Giving its users more news, assuming it's news they want to see, might be one way to wake them up.
Social media companies are also giving new thought to where people are reading the news. Mobile devices like smartphones and tablets are a popular place for that now. Facebook, in its announcement on Monday, said it was paying more attention to the number of clicks for articles on mobile.
The growth of news on social networks may be accelerating trends that are already underway. The days of opening a daily newspaper or clicking through a single news website such as CNN.com are on the wane, with search engines and news aggregation sites allowing people to dip in and out of multiple sites, some they are familiar with and others they are not.
One consequence is that people are able to zero in on the news topics that interest them most, by setting up personalized feeds from their favorite sources about, say, sports and politics. But that also means they're less likely to stumble upon news they're less interested in, such as international affairs.
As people get more news from social media, and those sites look for signals to determine which stories people will be most receptive to, is that a good thing? That depends partly on how savvy the reader is, Gilbert said. Questioning the source of an article has always been important, but readers must now also think about why social sites are presenting them only some news.
Having more options for receiving and discovering personalized content is a good thing, said Rick Edmonds, a media business analyst at the Poynter Institute for journalism training. But the shift of advertising dollars to online media has already cut down or eliminated print media that gave consumers news about their communities, he said.
And relying too heavily on a handful of sites like Facebook and Yahoo could leave people at the whims of a particular site's agenda. They're the same concerns people have always had with news media, but the rise of social sites gives the question a new dimension.