Thousands in the Tampa Bay area joined crowds across the state and nation Saturday to say "Never Again" — the mantra for many protesting gun violence since last month, when a school shooting in Broward County left 17 dead. Organized by students, the national event March for Our Lives has been the largest showing of mounting activism yet by teens pushing politicians to support stricter gun laws. Companion rallies to the one held in Washington, D.C., popped up throughout Florida, drawing a combined 15,000-plus to 11 events on both sides of the bay. That number inched close to that of St. Petersburg’s 2017 women’s march, where more than 20,000 people swamped downtown, marking the largest protest in the city’s history. By far, the single biggest local rally on Saturday was in downtown Tampa, where officials estimated attendance topped 13,000. Susana Matta Valdivies, a 17-year-old student from Marjory Stoneman Douglas High School in Parkland, where the shooting occurred on Feb. 14, addressed a crowd at Kiley Garden. RELATED COVERAGE: Hundreds of thousands expected today for Washington’s March for Our Lives Public speaking has always intimidated her, she said, but on Saturday, she knew what she had to say was more important than fear or embarrassment. And she didn’t stutter. "I still remember the fear and shock that went through us as we heard gunshots in school," the high school junior said. "To everyone who said it was too early for us to talk about politics: It was never too early ... Seven thousand children’s lives have been lost due to gun violence. We are not too early. We are 7,000 lives too late." For Valdivies and her classmates, the aftermath of the shooting has been marked by press interviews and protests. Their efforts yielded more than 800 student-led marches nationally Saturday, including about 50 in Florida, stretching from Tallahassee to Key West. To make the event in Tampa, where students from about 50 area schools came to join the chorus fighting gun violence, Valdivies ditched her spring break plans, bought herself a $47 plane ticket and stayed up until 2 a.m. Friday perfecting her speech. The students’ message is simple, she said: Ban automatic weapons and "bump stocks," devices that can speed up the rate at which semi-automatic rifles can be fired. Require background checks before a weapon is sold. Strengthen mental health services in schools. "Plenty of legislators are using mental health as an excuse for gun violence, but I have yet to hear any proposed solutions regarding it," said Sam Sharf, 17, a junior at Plant High School said to the crowd Saturday. RELATED COVERAGE: Live: Thousands descend on Tampa, St Pete and Washington for March for our Lives Mayor Bob Buckhorn also took the stage in Tampa, boldly backing the students’ cries. "I believe in the Second Amendment, but there is no reason why a hunter like myself would need an AR-15," he told the Tampa Bay Times after his speech. "I think a majority of gun owners would agree there’s nothing wrong with a waiting period; there’s nothing wrong with background checks; there’s nothing wrong with prohibiting citizens from owning weapons of war." He pointed students to voter registration booths stationed throughout the rally grounds, warning that their efforts will only effect change if they vote out of office politicians backed by the National Rifle Association. U.S. Rep. Kathy Castor, D-Tampa, who also attended the march, agreed. "Students need to know their power," she said. "When you look at who votes in America, they’re older and middle-aged. If (students) can put their passion into voting, they will spur meaningful change." Meanwhile, in St. Petersburg, about 1,500 people — ranging from poster-toting toddlers to senior citizens — gathered at Poynter Park with signs and shirts condemning the NRA. Enough is enough! Ban assault weapons, one read. What if ... you loved your KIDS more than your GUNS, said another. From her wheelchair, 90-year-old community organizer Winnie Foster watched it all unfold. "I had to come ... This is a big moment, not just for our city," she said. "I have been so impressed by these actions of change across the world." One visible opponent, Bob Teets, stood at the back of the crowd, holding a sign critical of the state’s new law that raised the age for rifle purchases to 21. "We are a constitutional republic and adults in America are 18 years old," said Teets, 56. "I think what (Gov.) Rick Scott did was unconstitutional." Mayor Rick Kriseman offered advice similar to Buckhorn’s, stressing to students the importance of voting. "It is tragic you all have to march for your young lives," he said, before leading the crowd into a chant: "Vote, vote, vote." Earlier in the day, Madison Vogel, a junior at Osceola Fundamental High School who helped organized the St. Petersburg rally, had a message for NRA-backed politicians. "Only half of us showed up to the polls, but that was before," she said. "We will vote you out of office like our lives depend on it." Like Valdivies, the Parkland student at the Tampa rally, Vogel said she stayed up late Friday night preparing for the St. Petersburg event. She woke hours before dawn to drive a U-Haul truck full of supplies downtown. "Our voices matter," she said. "We have a lot of adults telling us we don’t know what we’re talking about, but we know this better than they do because this is what’s happening to us." Elsewhere in Florida: the Orlando Sentinel reported an estimated 20,000 gathered at Lake Eola. In downtown Jacksonville, News4JAX reported "hundreds" in Hemming Park. The Tallahassee Democrat said "thousands" descended on the lawn outside the Capitol, in the same place others did a week after the Parkland shooting. Times staff writer Jonathan Capriel contributed to this report. Contact Megan Reeves at [email protected] Follow @mareevs.