Laundrie, 23, has not been charged with a crime, but police in his hometown of North Port, Florida, said they are now considering him a person of interest in a Wednesday tweet.
"As of now, Brian has not made himself available to be interviewed by investigators or has provided any helpful details," police said. "We know Brian returned here to North Port on September 1st — ten days before her family reported her missing on September 11th. We have no information that a crime occurred here in North Port."
The couple was traveling cross-country in their Ford Transit van and sharing photos and videos of their trip to social media. The 22-year-old Petito's mother reported her missing on Sept. 11, but they had last spoken in the final week of August.
Petito's family says he refused to tell them where he last saw her.
"Everyday the search for Gabby continues the Schmidt and Petito family becomes more desperate," Richard Stafford, the lawyer representing the Petito's mother, Nicole Schmidt, said in a Wednesday statement. "They are frantically searching for answers and information in their daughter’s disappearance while Brian sits in the comfort of his home."
Stafford continued: "Brian claims he wants to sit in the background while we search for Gabby in the wilderness of the Grand Teton and Yellowstone national parks. Brian left Gabby in the wilderness with grizzly bears and wolves while he sits in the comfort of his home. In his home! Brian, how could you do this to Gabby? You selfishly remain silent while Gabby is all alone in the wilderness. Brian, your silence is reprehensible! We beg you to do the right thing and help us bing Gabby home."
Police on Sept. 11 recovered the van that the couple was traveling in as part of their investigation, police said Wednesday. The investigation involves law enforcement agencies in multiple states and the FBI, the latter of which began a forensic examination on the vehicle Tuesday, North Port police told Fox News.
"As a father, I can imagine the pain and suffering Gabby’s family is going through. We are pleading with anyone, including Brian, to share information with us on her whereabouts in the past few weeks," North Port Police Chief Todd Garrison said in a Wednesday statement. "The lack of information from Brian is hindering this investigation. The answers will eventually come out. We will help find Gabby and we will help find anyone who may be involved in her disappearance."
Authorities are asking anyone with information about the case to contact the FBI's tip line at 1-800-CALLFBI (225-5324).
Fox News' Michael Ruiz contributed to this report.