SAN FRANCISCO – Facebook and most other social networks are built on the premise that just about everything should be shared -except the money those posts produce.

At least two services are trying to change that. Bubblews, a social network that came out of out of an extended test phase last week, pays users for posts that attract traffic and advertisers. Another company, Bonzo Me, has been doing something similar since early July.

“I just feel like everyone on social networks has been taken advantage of for long enough,” says Michael Nusbaum, a New Jersey surgeon who created Bonzo Me. “Facebook has been making a ton of money, and the people providing the content aren’t getting anything.”

Bonzo Me is paying its users up to 80 percent of its ad revenue for the most popular posts.

Bubblews’ compensation formula is more complex. It’s based on the number of times that each post is clicked on or provokes some other kind of networking activity. To start, the payments are expected to translate into just a penny per view, comment or like. Bubblews plans to pay its users in $50 increments, meaning it could take a while for most users to qualify for their first paycheck unless they post material that that goes viral.

“No one should come to our site in anticipation of being able to quit their day job,” Bubblews CEO Arvind Dixit says. “But we are trying to be fair with our users. Social networks don’t have to be places where you feel like you’re being exploited.”

Bubblews is also trying to make its service worthwhile for users by encouraging deeper, thoughtful posts instead of musings about trifling subjects. To do that, it requires each post to span at least 400 characters, or roughly the opening two paragraphs of this story.

Technology analyst Rob Enderle believes Bubblews, or something like it, eventually will catch on.

“I don’t think this free-content model is sustainable,” Enderle says. “You can’t sustain the quality of the product if you aren’t paying people for the content that they are creating. And you can’t pay your bills if all you are getting are `likes.'”

Gerry Kelly of San Francisco has already earned nearly $100 from Bubblews since he began using a test version in January. His Bubblews feed serves as a journal about the lessons he has learned in life, as well as a forum for his clothing brand, Sonas Denim.

Though Facebook is by far the largest social network, it has a history of irking users. People have complained when Facebook changed privacy settings in ways that exposed posts to a wider audience. They have criticized Facebook for circulating ads containing endorsements from users who didn’t authorize the marketing messages.

More recently, people were upset over a 2012 experiment in which Facebook manipulated the accounts of about 700,000 users to analyze how their moods were affected by the emotional tenor of the posts flowing through their pages. Facebook apologized.

Kelly still regularly posts on his Facebook page to stay in touch with friends and family, but says he is more leery of the service.

“They just take all your information and make all the money for themselves. It’s insane,” Kelly says.

Despite the occasional uproar, Facebook Inc. has been thriving while feeding off the free content of its nearly 1.3 billion users. The Menlo Park, California, company now has a market value of $175 billion, and CEO Mark Zuckerberg ranks among the world’s wealthiest people with a fortune of about $30 billion, based on the latest estimates from Forbes magazine.

Advertisers, meanwhile, are pouring more money into social networks because that is where people are spending more time, particularly on smartphones. Facebook’s share of the $140 billion worldwide market for digital ads this year is expected to climb to nearly 8 percent, or $11 billion, up from a market share of roughly 6 percent, or $7 billion last year, according to the research firm eMarketer.

Although it still isn’t profitable, short-messaging service Twitter is also becoming a bigger advertising magnet, thanks largely to its 255 million users who also provide a steady flow of free content. Twitter’s digital ad revenue this year is expected to rise to $1.1 billion, nearly doubling from $600 million last year, according to eMarketer.

Facebook and Twitter have become such important marketing tools that celebrities and other users with large social-media followings are being paid by advertisers to mention and promote products on their accounts.

Bubblews wants to make money, too, but it also wants to ensure that everyone using it gets at least a small slice of the advertising pie.

Dixit, 26, who started Bubblews with his college buddy Jason Zuccari, says the service got about 200,000 users during a “beta” test phase that began in September 2012. The service unveiled a redesigned website last week as it finally moved out of testing.

Bonzo Me is even smaller, with just a few thousand users since the release of apps for the Web, iPhones and Android devices in early July. The service has paid about $30,000 in ad revenue to users so far, according to Nusbaum.

Sandy Youssef of New Brunswick, New Jersey, likes being on Facebook, but she also intends to start posting video on Bonzo Me just in case she shares something that becomes a big hit.

“We are living in an age when the things you post on the Internet can go viral, so you may as well get paid for it,” she says. “It’s time to spread the wealth.”