The services at Moloney's Funeral Home in Holbrook was scheduled to be open to the public from noon to 5 p.m.
A large procession of mourners were seen arriving for the memorial to pay their respects to Petito and her family.
Mourners arrive for Gabby Petito memorial
Footage from a livestream of the event Sunday provided by the funeral home showed an altar surrounded by pictures of Petito. Attendees walked by, eyeing the photos, while others gathered, hugging and talking.
In a eulogy, Joseph Petito described his daughter as a "happy girl," who people would gravitate toward. She made others feel welcome, he said, and loved adventuring outdoors, whether it was scuba diving or hiking the Appalachian Trail.
"I want you to be inspired by Gabby, that's what we're looking for," Joseph Petito said. "If there's a trip that you guys want to take, take it now. Do it now while you've got the time."
"If there's a relationship that you're in that might not be the best thing for you, leave it now," he said, an apparent reference to his daughter's relationship with Laundrie.
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Petito said his family has received emails from people all over the country who are leaving relationships because of what happened to Gabby. Petito said people are "putting themselves first."
Petito's stepfather, Jim Schmidt, also gave eulogy, telling those gathered, "Parents aren't supposed to bury their children. That's not how this is supposed to work."
Schmidt said he hopes Gabby's love of people inspires people to love others.
"She is an example of all of us to live by," he said.
Outside, signs posted across the street bore Petito's name and read, "Forever in our hearts."
Attendee Angelina Amendola said she didn't know Petito personally. But they came from the same hometown, Blue Point, and she wanted to support Petito's family.
"I'm a mother -- I could never imagine something like that happening to my boys," Amendola told CNN.
"It's going to be a lot," she said of the memorial. "But I want to show the Petito and Schmidt family lots of love and let them know that they're surrounded by people who love them and care for Gabby."
Many young people, Petito's age, attended her memorial Sunday, including Melanie McGuire.
"She was a beautiful person, beautiful soul," McGuire said. "I'm heartbroken."
Sonja Greves knew Gabby since middle school.
"It's really such a shame," Greves said. "She was such a kind soul."
Petito's remains are still in Wyoming. The coroner has not yet determined her cause of death.
FBI visits Laundrie house, asks for items belonging to Brian
The FBI said investigators are still seeking information from anyone who may have seen the Gabby Petito and Brian Laundrie around Grand Teton.
On Sunday, the Laundrie family attorney said Sunday that "The FBI requested some personal items belonging to Brian Laundrie to assist them with DNA matching and Brian's parents provided the FBI with what they could."
The attorney says it's "routine."
Gabby Petito Foundation created
On Saturday, Petito's father, Joseph Petito, announced the creation of 'The Gabby Petito Foundation.'
In a tweet, he said the foundation will give resources and guidance to families of missing children.
"No one should have to find their child on their own," he said, "we are looking to help people in similar situations as Gabby."
A link to the Gabby Petito Foundation can be found here.
Petito vigil held Friday night
A vigil was held Saturday night in Florida for Gabby Petito.
People who were touched by her story gathered in North Port - home to Brian Laundrie and his family. Those in attendance say they want justice for Gabby, and they had a message for her parents.
Gabby Petito's mother, Nicole Schmidt posted to Facebook following a 12-day silence.
She wrote, in part,
"As I scroll through all the posts, my heart is full of love. I wish I could reach out and hug each and every one of you. Your support has been so overwhelming."
On Friday, residents of Blue Point resolved to find light in the dark tragedy. They lit candles for Gabby Petito in a memorial that stretched as far as the eye could see - to show her family they aren't alone.
Long Island residents light candles in honor of Gabby Petito
Organizers spread the word of "Light the Night For Gabby Petito" in the hopes the event will not only spread across Long Island but also the country.
The candles were being given out along with a request for a $20 donation, with the proceeds going to Gabby's family.
Information from CNN was used in this report.
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