Michael Stewart endured three months of night sweats, vertigo and weight loss before he finally went to a free health clinic in San Francisco.

Blood and urine tests showed nothing, so the clinic staff sent him to San Francisco General Hospital. That’s when the bills began accumulating — blood test, X-ray, endoscopy, two colonoscopies, two MRIs, two CAT scans and 10 days in intensive care. And the 48-year-old Stewart didn’t have health insurance.

The full-time actor was thousands of dollars in debt before he even received his diagnosis: stage three colon cancer.

What he did next is something researchers say has become almost routine among the medically uninsured: He turned to a popular fundraising website to raise money.

His first pitch was 811 words.

“My living expenses soared this year,” he wrote on GoFundMe, the San Diego crowdfunding platform that helps people raise money for everything from art projects to cancer treatments. “I come to this site as a last ditch effort to keep surviving this.”

Nora Kenworthy, a researcher at the University of Washington who, along with colleague Lauren Berliner, has studied hundreds of GoFundMe medical campaigns, said the cost of health care is driving more people to fundraising sites.

“There are a lot of people cobbling things together to make ends meet,” Kenworthy said. “The social safety net is not quite catching everyone.”

Medical and health-related causes are the most popular category on GoFundMe, with more than $930 million raised from 2010 to 2016.

“We’ve now reached a point in popular culture where ‘GoFundMe’ has become shorthand for help,” Rob Solomon, GoFundMe’s CEO, wrote in his annual year-end letter on the site. “What do you do when your neighbor has fallen on hard times or your child’s classroom needs books? You start a GoFundMe.”

YouCaring, a crowdfunding website in San Francisco, is the second most popular site for medical campaigns. YouCaring executives said they have seen a 25 percent increase in medical campaigns on their site since 2014. Jesse Boland, YouCaring’s online marketing director, projects the same growth for next year.

Stewart’s first acting role was as an extra for the 2011 film “Contagion.” When the shoot ended, he walked back to his car and knew acting was for him.

“I was pounding the steering wheel, saying, ‘I got to do this again,’” he said.

When he got home that evening, he Googled “how to be an actor in San Francisco” and found SF Casting, a network of actors, directors and producers that post audition opportunities. Stewart applied and applied again until he started picking up regular gigs.

“Acting totally changed my life,” he said. “All of the things I wanted to be as a kid, I’ve gotten to be.”

Stewart was virtually broke as he worked to make ends meet as an actor. Eventually, his medical insurance premiums got too high and he decided to drop the insurance. He had never been seriously sick before and didn’t think he would need it, he said. So when he started experiencing symptoms in November, he waited.

“The first time I had a symptom, if I had coverage, I would have gone straight to the doctor,” he said. “I was hoping it would go away in a week or two.”

When his health started seriously deteriorating this year, Stewart stopped picking up acting roles. And when a few months later he couldn’t walk without getting winded, or couldn’t climb the ladder to his bedroom loft, he moved back in with his parents.

Now, Tom and Pat Stewart take care of their son full time. They drive from their home in Morgan Hill to San Francisco General, where Stewart has been hospitalized for about three weeks. They attend nearly all of his appointments and cook homemade meals to bring his weight back up. He’s lost about 75 pounds, leaving him just over 100 pounds.

“If he wasn’t my son and I just saw him, I wouldn’t know who he was,” his mother said. “He looks so different.”

Tom and Pat Stewart are retired teachers, living on fixed incomes and Medicare. When their son received his diagnosis, they didn’t know what to do.

“There was no way we were going to be able to financially help him,” his mother said.

So when their son told them he was considering a GoFundMe page, they encouraged him to do it.

At first, donations poured in. He raised $7,000 in the first 10 days. All of the donations, ranging from $5 to $500, came from friends or family. People from his past chipped in — kids he grew up with in Florida and the South Bay, friends he hasn’t seen for years, and fellow actors.

But now, two months later, donations have tapered off to just one every few days.

“I’ve been trying to explore other ways of marketing myself,” he said. “I’ve more or less marketed myself to death to my friends.”

Researchers say once a campaigner’s network runs dry, the only place to turn is strangers, and that’s when the market for sympathy can get competitive. Because as the number of campaigns increases, there’s going to be even less money to go around, Berliner said.

Seeming worthy of a donation can come down to how compelling a person’s story is or the quality of his or her pictures. Crowdfunding websites include tips on how to have the most successful campaigns: an interesting video, frequent updates, a catchy title. These can often be the difference between a campaign raising $100 or $1,000.

Berliner and Kenworthy saw these factors play out in their study of GoFundMe medical campaigns. Successful campaigns were largely based on the strength of the person’s network — how many people they knew and how many friends and acquaintances were willing to share the campaign on their own social media. And those who could describe their medical needs in not only a clear way, but in an interesting way, received the most money.

San Francisco resident Dennis Disbot positions himself in the successful category. He raised more than $50,000 on YouCaring after he was diagnosed with an aggressive form of testicular cancer in 2015.

He had a compelling story to start. Hours before his scheduled surgery to remove his tumor, his pregnant wife went into labor. After he rescheduled it a few days later, his newborn son, Theo, was admitted to the hospital for jaundice. Disbot finally checked into the hospital for his surgery as his wife and son were leaving from Theo’s stay.

After doctors removed his tumor, Disbot started chemotherapy to clear the cancerous cells in his bloodstream. Bills were piling up when he started his fundraising campaign in November 2016.

A friend who worked for a film crew offered to create a video to tell their story. The professional quality of the video paired with Disbot’s story is what made the campaign so successful, he said.

Donors connected with him through the video, which was shared widely on social media. Disbot did have health insurance, but the campaign helped cover unforeseen costs — hearing aids when the treatment caused a constant buzzing in his ears, and child care when he and his wife couldn’t be there for Theo.

“Before we went to YouCaring, we were scraping the barrel,” he said. “I only wish I had asked for help sooner.”

Not only did Disbot’s video help connect him with strangers, it also added veracity to his campaign. With multiple cases of people using crowdfunding to make money from fake illnesses or projects, donors could be more sure Disbot was telling the truth.

Crowdfunding websites GoFundMe and YouCaring do not guarantee that all campaigns are legitimate. Both websites rely on users to flag campaigns they find suspicious, but state directly on their websites there is no way to completely verify the truthfulness of a user’s claims.

GoFundMe’s website states that fraudulent campaigns make up less than one-tenth of 1 percent of all campaigns — a minuscule portion of the hundreds of thousands of campaigns on the site.

When Stewart updates his GoFundMe page, he almost always includes a picture from before this all started. Photos of him as a baby, sailing on a boat in Hawaii, or when he was on set, acting in San Francisco.

“I’m a little slow and (it) takes some effort to rise out of chair, climb the stairs or get out of a small car,” Stewart wrote in his seventh update. “But that will change.”

Below it is a photo of Stewart from 2011, when his 6-foot-2 frame weighed 180 pounds, not 104. In the picture, roles are reversed. He stands over a hospital bed wearing scrubs and a stethoscope instead of lying on it under a thin, white blanket.

It’s hard to ask for help, he said. Swallowing your pride and holding out your hand isn’t easy. But Stewart felt he had few options.

He recently applied and was approved for Medi-Cal, but is unsure how much it will cover. Meanwhile, he has raised almost $9,000 of his $35,000 goal.

“I’ve reached the end of my audience,” Stewart said. “At least I know that the amount I’ve raised right now will take a lot of weight off my back for the next few months.”

The money will not only pay for his treatment but also help him keep his apartment on Potrero Hill. Rent and other basic expenses cost him about $1,750 a month.

He has had chemotherapy but needs radiation therapy. Complications — a blood clot, a burst abscess and emergency surgeries — have delayed the start of his radiation. He is recovering at San Francisco General Hospital from a bone-deep wound after an abscess burst near his tumor. And more charges add up every day.

“Any amount is appreciated as always and thank you for all those that showed their support and generosity,” he wrote in his latest GoFundMe update.

The photo underneath shows a 25-year-old Stewart looking into the viewfinder of a camera. He has long, blond hair and a white bandanna around his head. The camera lens is pointed at lava flows in Hawaii, where he worked as a volcano photographer in the 1990s. He bought a one-way ticket at 22 and he didn’t leave for 20 years.

He said those years were the best of his life — before he worried about cancer, radiation treatment or how he’s going to pay for it all.

And it’s where he plans to go when he beats the cancer.

Alison Graham is a San Francisco Chronicle staff writer. Email: agraham@sfchronicle.com Twitter: @alisonkgraham