Two sisters of slain teacher Victoria Soto asked the crowd gathered at Edmond Town Hall for a 26-second moment of silence, honoring the 20 children and six adults gunned down at the school on Dec. 14.
"This pain is excruciating and unbearable but thanks to people like you, that come out and support us, we are able to get through this," said Carlee Soto, who held hands with sister Jillian before taking the stage.
The event then transitioned to the reading of the names of more than 6,000 people killed by gun violence since the tragedy in Newtown. The reading of names is expected to take 12 hours.
Mayors Against Illegal Guns, which organized the event in Newtown, also launched a bus tour that will travel to 25 states over 100 days to build support for legislation to expand background checks for gun buyers. Such legislation failed in the Senate in April.
The mayors group is also holding events in 10 states calling for lawmakers to expand background checks and urging senators who opposed the bill to reconsider. Those events, which include gun violence survivors and gun owners, will be held in Arkansas, Arizona, Florida, Georgia, Indiana, Montana, North Carolina, New Hampshire, Ohio and Pennsylvania.
The gunman in Newtown killed his mother and then the 26 people at Sandy Hook Elementary School with a semiautomatic rifle before committing suicide as police arrived.
Some of the victims' families are in Washington this week lobbying lawmakers for action. Jillian and Carlee Soto met with President Barack Obama as they campaign for gun control.
"He just told us to have faith," said Jillian Soto, 24. "It isn't something that happens overnight. It's something that you have to continue to fight for. Within good time we will have this passed and we will have change."
New York Mayor Michael Bloomberg, who co-founded the mayors group, this week sent a letter asking donors not to support Democratic senators who opposed the bill to expand background checks.
On the other side of the debate, the National Rifle Association is focusing on Sen. Joe Manchin, D-W.Va., who co-sponsored the bill to expand background checks, with a TV ad urging viewers to phone Manchin's office and tell him "to honor his commitment to the 2nd Amendment." The NRA plans to spend $100,000 airing the ad in West Virginia markets over the next two weeks.