Sara Azar, an attorney representing the family, said the scam marriage information is based on an internet tip sent to Kobayashi's sister.
"They found on Reddit that Hannah had been married, and it was some sort of arranged marriage for money type of situation, essentially for a green card," Azar explained. "Hannah's sister immediately turned over that information to law enforcement."
The FBI told Eyewitness News it has been assisting the Los Angeles Police Department, which is leading the investigation.
As for the allegations of a bogus marriage, LAPD said it is aware of the claims but it had no impact on the investigation.
LAPD announced this week that Kobayashi was seen on video safely crossing the border into Mexico on Nov. 11, four days after she landed at LAX. Chief Jim McDonnell said there is no evidence Kobayashi was being trafficked or was otherwise a victim of a crime. Her disappearance is now classified as a "voluntary missing person," he said.
According to McDonnell, Kobayashi disappeared voluntarily as she sought to "step away from modern connectivity."
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Kobayashi's aunt Larie Pidgeon believes her niece is still in Mexico, and that it's been nearly a month since Kobayashi has spoken with any family or friends.
"I and my family have parted ways at this point... My only goal is to make sure Hannah is safe and doing this on her own accord," Pidgeon said in a statement to Eyewitness News.
Meanwhile, the rest of the Kobayashi family is expecting additional surprises.
"I think there will be more twists to be honest with you," Azar said. "It's so unusual that she would plan this trip and be in contact with her family in New York and look forward to it and then just completely divert and go off the grid."
Kobayashi's family released a statement Wednesday after a Los Angeles Magazine report said the family was investigating if she was involved in a possible immigration marriage scam.
"We want to stress that the family has not publicly announced any information regarding an alleged marriage because we did not have the facts or the necessary documents to verify the legitimacy of this information," the statement said in part. "The family has not confirmed the authenticity of the images or the accuracy of the information provided about a possible secret marriage."
Kobayashi flew from Maui to LAX on Nov. 8 and was expected to take a connecting flight to New York but missed that connection. Aside from a few cryptic text messages the family has not heard directly from her.
Police later said they believe she missed the connecting flight on purpose. She retrieved her luggage from LAX days later, used cash and her passport at Union Station to buy a bus ticket to the border before walking into Mexico.
Hannah's father, Ryan Kobayashi, was found dead last month in a parking lot near LAX. The medical examiner determined the cause of death to be suicide.
The Associated Press contributed to this report.