Now, authorities say they have a lead in the case, with police having served a search warrant overnight at the home of a "person of interest."
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Outside the house, police set up a mobile command center and apparently searched the house for hours.
While the police have not named any suspects, Salt Lake City Assistant Police Chief Tim Doubt said in a press conference that residents of the house are being investigated.
“Of course they are a part of this investigation,” Doubt said Wednesday night, but added Thursday morning in a press conference that no arrests were made and police are not identifying the homeowner at this time.
Police also announced that based on tips from residents, they are looking for a mattress and box spring from the home they think is connected to the case.
Police say that the Lyft driver and the ride-share company have been cooperative in the investigation, and that the department is in communication with Lueck's family.
"I can feel the heartache and the pain and the suffering in his voice as we spoke," Salt Lake police chief Mike Brown said of his conversation with Lueck's father, adding that the department is doing "everything within our power ... to bring Mackenzie home."
Authorities asked anyone with information to contact them as they continue the investigation into Lueck’s disappearance.
Ben Kesslen is a reporter for NBC News.
Janelle Griffith is a breaking news reporter for NBC News.