The case of a Missouri couple who vanished from their remote home has left law enforcement scratching their heads and relatives pleading for their return.

Leo Lindeman, 73, and his wife, Katherine Lindeman, 74, were last seen on September 15 and are believed to have disappeared a day later, according to the McDonald County Sheriff's Office. 

The couple lives with a small white dog named Itty Bitty in a rural home near Anderson, a small city in southwestern Missouri's Ozark foothills. 

The dog has vanished along with its owners, police said. The Lindemans were formally reported missing on September 24, though authorities did not say who submitted the report. 

The husband and wife are 'private people,' so it was not strange that their neighbors hadn't heard from them for a while, McDonald County Sheriff Robert Evenson told KNWA.

'We’ve got a bit of a mystery,' he added.  

As the investigation unfolds, Leo's sister, Leza Lindeman, told the outlet: 'We do love our brother and that’s why we’re here, is because we’re worried about them.'

'If anybody has any information, even if you think it’s not important, please do give the police a call,' she added with a trembling voice. 

The sheriff said his office obtained a search warrant for the Lindemans' home a few days after they were reported missing. 

Police have dusted for prints in the residence and collected electronics and trace evidence that may be helpful for the investigation down the line, Evenson told KNWA.

Authorities also searched the area around the home and nearby properties, he said.

Leo's niece, LaShawnda Lindeman, wrote in a Facebook post on Wednesday that police and family members have been searching the area around the house for days.

She said that on Monday, family members went to the residence with a private drone operator who flew over the area from 6am to 11am before a search and rescue team with a dog came to assist for several more hours. 

Then on Tuesday, more family members returned to the property. 

They, along with the sheriff's office and another company that brought two additional drones, three more search dogs and a large team of people, continued to search the whole day, LaShawnda said. 

'Together, approximately 15 acres of property were extensively searched. Unfortunately, we did not find Leo, Katherine, or anything that gave us answers as to where they may be,' she said. 

'We are incredibly grateful to everyone who has helped search, shared their information, reached out, or offered support. Please continue sharing and helping us get the word out,' LaShawnda continued. 

'We just want to bring them home and get answers,' she concluded her post. 

Sheriff Evenson told KODE12 that the investigation is ongoing, though there has been a 'frustrating' lack of evidence or leads thus far. 

'We'd like to have some leads, some solid leads, that will get us moving in the right direction, and I'm hopeful that will happen,' he said.