Matt Parks knows there is someone out there with a bone marrow match for Hayley Desjardins.

“We just need to find them,” said Parks, the development director at Maine Medical Center in Portland.

Hayley, an active 12-year-old from Saco, is in critical, urgent need of a bone marrow transplant to treat a rare blood disease, said Parks, who is a friend of her family. While schoolmates at Thornton Academy and others in the Saco community have rallied to support the family, her need for a bone marrow match has prompted hundreds of people – including many strangers – to sign up to be tested as possible donors. Advocates say the case is bringing needed attention to the chronic shortage of potential donors who might help patients such as Hayley.

“When we have someone like Hayley that people can connect with, it helps people understand how they or their own family could be impacted. It brings it close to home,” said Ashley Cox, a donor recruiter with Delete Blood Cancer, the organization that registers potential bone marrow donors.

Hayley was first diagnosed with aplastic anemia at age 6 and endured repeated hospitalizations and blood transfusions. Her treatment was deemed a success in 2009, but in October 2014 the family learned that Hayley had suffered a relapse.

Aplastic anemia occurs when the body stops producing enough new blood cells. It affects just one or two out of a million people each year, according to St. Jude Children’s Research Hospital. The disease leaves the patient feeling fatigued and at a higher risk of infections and uncontrolled bleeding. It can be successfully treated but also tends to get worse over time and severe cases can be life-threatening.

Hayley has been receiving treatment at the Barbara Bush Children’s Hospital in Portland and at Boston Children’s Hospital. Her doctors have said her best treatment option is a bone marrow transplant.

While Hayley was in the Boston hospital last Monday with her mother, Allison, more than 375 people braved a snowstorm to show up at Maine Medical Center during a donor registration drive organized to try to find her match. They waited in line to have the insides of their cheeks wiped with cotton swabs, which collect cells that can be analyzed in a lab.

Regina Martin of Woolwich showed up with her daughter in tow. They have never met Hayley, but after Martin heard her story there was no way she’d miss a chance to save her life.

“When I saw a picture of her on Facebook, it really struck home,” she said. “I’d want someone to help my daughters or son.”

During two events the weekend before in Saco and Biddeford, about 400 people registered. The three events are the latest of 32 bone marrow registry sessions scheduled in Hayley’s name since she became sick again.

“I am so proud to be a part of such a strong community in Maine,” Mike Desjardins, Hayley’s father, said in an email message from the Boston hospital where his daughter is being treated. “We are so grateful for everyone’s support.”

Hayley is well known in Saco because of her previous battle with aplastic anemia and the “Hugs for Hayley” 5K fundraiser set up to support her family and other chronically ill children. After she finished treatment in 2009, she set out to raise money for the Maine Children’s Cancer Program, where she had received treatment.

Since 2008, the Desjardins family has raised $70,000 for the Maine Children’s Cancer Program through the Hugs from Hayley races. Mike Desjardins is on the program’s board of directors.

Finding a bone marrow match is much more difficult than finding someone with a matching blood type.

Every year, more than 140,000 Americans need bone marrow transplants as life-saving treatment for blood cancers and about 70 other diseases, including aplastic anemia. Fewer than half of them will find their match, according to Delete Blood Cancer.

Most who find a match get the bone marrow from strangers, but only 2 percent of Americans are on the National Bone Marrow Registry, Parks said.

When word got out that Hayley needed a bone marrow transplant, supporters took to social media to share her story and encourage people to see if they were a match. Posters advertising her bone marrow registry drives hang around Saco, often featuring photos of a smiling Hayley with her younger sister, Maddison , wrapped against her in a hug.

At Thornton Academy, where Hayley plays youth basketball, students rallied around the family. The school’s international boarding students raised money to buy Hayley an iPad to use during extended hospital stays. The girls’ basketball program launched “Hoops for Hayley” and, over the course of the season, raised $10,000 for the Desjardins family.

Parks, from Maine Medical Center, said the Desjardinses and their supporters remain optimistic they will find a match for Hayley. Their hopes are buoyed, he said, by the hundreds of people who show up each time they put out a call for potential donors.

“It will either save Hayley’s life or someone else’s life,” he said. “We’re very confident we will find a perfect match for Hayley.”

People who are between 18 and 55 and in relatively good health are eligible to register as a potential donor. After filling out a simple form, the insides of their cheeks are swabbed to collect cells to determine tissue type. Delete Blood Cancer will send registration kits to anyone who can’t make it to a scheduled event.

“It only takes 5 to 10 minutes,” Cox said. “And this can directly save someone’s life.”

When people register, they have the potential of donating either bone marrow or blood stem cells, depending on the need of the patient. A blood stem cell donation is more common and is a non-surgical, outpatient procedure. A bone marrow donation requires a one- to two-hour surgical procedure under anesthesia so that marrow cells can be collected from the back of the hip bone using a syringe.

To register as a potential donor, go to www.deletebloodcancer.org.