The family of missing woman Gabby Petito, who was last heard from while on a road trip with her fiancé late last month, is begging Brian Laundrie and his family to come forward and share information that could help them in the search. 

"We believe you know the location where Brian left Gabby. We beg you to tell us," a letter read by the family's lawyer at a press conference Thursday said.

"Gabby lived with you for over a year. She was going to be your daughter in law. How can you keep her location hidden? Please, if you or your family have any decency left, please tell us where Gabby is located. Tell us if we are even looking in the right place."

22-year-old Gabby Petito from New York's Long Island was reported missing on Saturday by her family after her fiancé returned home alone from a cross-country road trip the two had embarked on in early July. Police and Petito's family say the fiancé, Brian Laundrie, is refusing to speak to law enforcement

22-year-old Gabby Petito from New York's Long Island was reported missing on Saturday by her family after her fiancé returned home alone from a cross-country road trip the two had embarked on in early July. Police and Petito's family say the fiancé, Brian Laundrie, is refusing to speak to law enforcement (Steve Petito )

Petito and Laundrie, who have been engaged since last year, left the Florida Gulf Coast town of North Port in June for New York, then headed out west in early July. 

Petito's family stopped hearing from her in late August. 

Meanwhile, Laundrie returned home to Florida with the white van they were traveling in on Sept. 1, but has since hired a lawyer and is not cooperating with authorities. 

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A lawyer for Petito's family said that the Laundries refused to answers messages on Sept. 10 and 11 before she was reported missing. 

"The family is devastated. Every day that this goes on, they get more and more desperate," the attorney said at a press conference Thursday. 

"They’re at the point that desperation is turning to anger. They know that the Laundries know where their daughter is and they will not tell them. That's infuriating."

Gabby Petito and Brian Laundrie (Credit: Fox News Instagram screenshot)

Gabby Petito and Brian Laundrie (Credit: Fox News Instagram screenshot)

North Port police chief Todd Garrison also shared his frustrations with Laundrie's lack of cooperation, even calling out his lawyer, Steven Bertolino on Twitter this week. 

"We share the frustration with the world," Garrison said Thursday. "Two people went on a trip, and one person returned. That person who returned isn’t providing information."

Bertolino put out a statement on Tuesday saying that the Laundrie family hopes Petito is found safe. 

"On behalf of the Laundrie family, it is our hope that the search for Miss Petito is successful and that Miss Petito is reunited with her family," Bertolino said. "On the advice of counsel, the Laundrie family is remaining in the background at this juncture and will have no further comment."

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Petito's stepfather, Jim Schmidt, called Laundrie's lack of cooperation "mind-boggling" on Thursday. 

"You say she’s the love of your life. She’s missing. You were on a trip with her, but you have no comment. You have nothing to say and you’re hiding behind an attorney," he told Fox News on Thursday.

"I understand the constitutional rights that people have, but you have pieces to this puzzle that we need to find Gabby and you’re withholding them from us."