In a troubling sign that more young Americans are struggling with depression and anxiety, new research shows a significant rise in the number of school-age children and teens thinking of taking their own lives or actually attempting suicide.

The study, published in the journal Pediatrics, found that the number of kids and teens hospitalized for suicidal thoughts or attempts more than doubled in the U.S. from 2008 to 2015.

"There are increasing rates of anxiety and depression in youth and young adults. Some people have theorized that social media is playing a role," study author Dr. Gregory Plemmons, an associate professor of pediatrics with the Monroe Carell Jr. Children's Hospital at Vanderbilt University, told CBS News.

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The study looked at trends in emergency room and inpatient visits for suicidal thoughts and suicide attempts in young people between the ages of 5 and 17 at children's hospitals in the U.S..

Overall, the researchers identified nearly 116,000 such cases at 31 children's hospitals. About two-thirds of those cases involved girls. Increases were seen in all age groups, but were highest among teens aged 15 to 17, followed by ages 12 to 14.

The study also found higher rates for suicidal thoughts and attempts occurred in the fall and spring, a pattern that suggests school may play a role.

Plemmons said he was not surprised by the findings, as previous studies have shown reported a dramatic increase in the prevalence of anxiety and depression among young people.

Suicide is now the third leading cause of death among American adolescents, the study authors point out.

Experts say it's important to know the warning signs.

"Certainly major changes in sleep and appetite can be red flag," Plemmons said.

There's also evidence social media may play a role. "We know that increasing screen time on electronic devices is a marker for depression, as well, so talking to teens about their use of media is important," he said.

In response to these disturbing trends, some students are trying to start a national conversation about the mental health of teenagers. At Bellport High School in New York, Taylor Fontana, Savanna Borrero, and Alexis Walker helped organize a mental health awareness week in remembrance of their friend, 15-year-old RJ Buada, who died by suicide last summer.

"He would just light up a room with his smile," Fontana said.

"I remember hearing the news and just thinking 'why?'" said Borrero.

For the campaign, they posted positive messages around their school, such as, "You're important, your life matters, your thoughts matter" and "Your story isn't over yet."

The students say by talking about this taboo topic, they hope they can help break down the stigma.