Data highlighted in the study include:
—Teens' use of electronic devices including smartphones for at least five hours daily more than doubled, from 8 percent in 2009 to 19 percent in 2015. These teens were 70 percent more likely to have suicidal thoughts or actions than those who reported one hour of daily use.
—In 2015, 36 percent of all teens reported feeling desperately sad or hopeless, or thinking about, planning or attempting suicide, up from 32 percent in 2009. For girls, the rates were higher — 45 percent in 2015 versus 40 percent in 2009.
—In 2009, 58% of 12th grade girls used social media every day or nearly every day; by 2015, 87% used social media every day or nearly every day. They were 14% more likely to be depressed than those who used social media less frequently.
"We need to stop thinking of smartphones as harmless," said study author Jean Twenge, a psychology professor at San Diego State University who studies generational trends. "There's a tendency to say, 'Oh, teens are just communicating with their friends.' Monitoring kids' use of smartphones and social media is important, and so is setting reasonable limits, she said.
Dr. Victor Strasburger, a teen medicine specialist at the University of New Mexico, said the study only implies a connection between teen suicides, depression and social media. It shows the need for more research on new technology, Strasburger said.
He noted that skeptics who think social media is being unfairly criticized compare it with so-called vices of past generations: "When dime-store books came out, when comic books came out, when television came out, when rock and roll first started, people were saying 'This is the end of the world.'"
With its immediacy, anonymity, and potential for bullying, social media has a unique potential for causing real harm, he said.
"Parents don't really get that," Strasburger said.
AP reporter P. Solomon Banda contributed to this story from Littleton, Colorado.
Follow AP Medical Writer Lindsey Tanner on Twitter at @LindseyTanner .