The father of a 14-year-old girl who was gunned down in Parkland, Florida, has called on President Donald Trump to address threats against student survivors and their families – many of whom have been outspoken about their desire for tighter gun-control laws since the deadly shooting at Marjory Stoneman Douglas High School.

Some have been harassed (or worse) by gun-rights advocates; others have become the target of viral lies and even death threats.

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On Wednesday, as students returned to school for the first time since the horrific shooting that left 17 people dead, Fred Guttenberg spoke to CNN about the occasionally vicious attacks against the survivors.

"There's been threats against some of these kids and their families," said Guttenberg, whose daughter, Jaime, was among the victims.

"We need our President Trump today to address it publicly and demand that everyone who is making these threats stop," he said.

He said he hoped the FBI, Broward County Sheriff's Office and other authorities were investigating the threats – "and initiating arrests."

"This community has been through trauma," Guttenberg said. "We can't have additional trauma in this community. . . . We need to get something done."

Read more: Parkland survivor David Hogg on conspiracy theories: 'It's sad'

He added: "Trump, make an announcement."

Since the shooting, some student survivors have pushed for tougher gun-control laws, traveling to Tallahassee and Washington in an attempt to discuss gun-control efforts with legislators. They also have been tangling with conservative critics and trolls on Twitter and organizing a nationwide march.

Their activism has made them targets, and conspiracy theories have alleged that the vocal students are "crisis actors."

There have been threats, too: Cameron Kasky, a junior at the school, wrote last week that he was leaving Facebook temporarily because "the death threats from the @NRA cultists are a bit more graphic than those on twitter."

Rebecca Boldrick, whose 17-year-old son David Hogg has become one of the school's most prominent student-activists since the shooting, said she had initially scoffed at the conspiracy theories.

But then the family started receiving death threats, she told The Washington Post.

"I'm under so much stress," she said a week after the shooting. "I'm angry and exhausted. Angry, exhausted and extremely proud."

The major social media platforms have also responded to harassment against the students.

"Such behavior goes against everything we stand for at Twitter, and we are taking action on any content that violates our terms of service," the company tweeted.

Trump doesn't always respond to public pressure to speak out about interactions between Americans – but he has done so on occasion.

Most notably, in late 2016, after the election, "60 Minutes" correspondent Lesley Stahl asked the president-elect about a reported spike in incidents of racial intimidation and harassment across the country.

And for the first time, Trump addressed reports of hate crimes committed in his name.

"I am so saddened to hear that. And I say: Stop it," Trump told Stahl. "If it, if it helps. I will say this, and I will say right to the cameras: Stop it."

On the day of the shooting, Guttenberg posted on Facebook that he found his son but could not reach his daughter.

The next morning, he wrote that his "heart was broken." He and his wife had "lost our baby girl to a violent shooting at her school."

"Hugs to all and hold your children tight," he wrote.

Since then, he has taken on a prominent role among Parkland parents.

At CNN's emotionally charged town hall on gun violence last week, Guttenberg confronted Sen. Marco Rubio, R-Fla., on the lawmaker's gun-control stance.

"I want to like you," Guttenberg told the senator. "Here's the problem. And, I'm a brutally honest person, so I'm just going to say it up front.

Read more: Rubio faces tough audience at CNN forum, backs some gun restrictions while refusing to disavow NRA

"Your comments this week, and those of our president, have been pathetically weak."

On Wednesday, Guttenberg talked about returning to Stoneman Douglas without his daughter.

"My son walks in here without his sister," he told CNN. "My daughter's friends walk in there. They used to always walk in with my daughter . . . and they're walking in there without her."