Once you've joined Disney's Mickey Mouse Club – especially the 1950s original – you'll never be forgotten, which makes the mysterious disappearance of former Mouseketeer Dennis Day seven months ago all that more baffling.

Day, 76, a Mouseketeer for two years in the mid-1950s, was once among the most famous child performers on American television, dancing and singing on millions of black-and-white TVs across the nation, wearing the iconic mouse-ear beanie and sweaters emblazoned with his name.

But Day has not been seen since July, when he vanished from his small town of Phoenix, Oregon. He left behind his beloved cat and dog and his partner of more than 45 years, Ernest Caswell, who had been hospitalized after a fall, according to Lt. Jeff Price, second-in-command of the seven-member police department in Phoenix.

His sister, Nelda Adkins of Coalinga, California, fears the worst.

"The way it looks now, unless we find a body, we're not going to find him," she told USA TODAY.

The signs are not good, according to Price. Day's bank account appears safe and untouched. His car was found about 200 miles away on the Oregon coast in the possession of two strangers who claimed Day had let them borrow it.

It was impounded by Oregon State Police and later searched, but there was no sign of foul play, Price says. Now he's trying to track down the man and woman who were found with the car.

A temporary roommate insisted he didn't know Day's whereabouts, although Price says he had Day's debit card.

Day's husband, who suffers from dementia-related memory problems and now lives in assisted care, could shed no light except to say that Day had told him he was going to visit friends on the day of the fall and his disappearance. Police were not alerted that Day was missing until two weeks after he was last seen.

Day has not contacted his friends in southern Oregon, near the border with California, nor his nephew in the area, nor his sister, who lives near Fresno, California. In fact, his friends and family didn't even know he was missing until January, Adkins says, when an Oregon TV news program aired a story about Day's disappearance.

Day's ramshackle rural home and property have been searched. So have a local cemetery and canals, including with cadaver dogs. Police are stumped, Price says, because they don't know where to look in a vast potential search area containing woods and rivers.

Price said he met with county sheriff's deputies and Oregon state troopers to brainstorm ideas for pursuing the case, but it didn't help when one of them wondered: "What's a Mouseketeer?"

"It's a nightmare of a case," says Price, who knows who the Mouseketeers were. "He just up and left, and we have no idea what direction he went or if he left voluntarily or not."

(In 1989, Disney revived the series as the "All-New Mickey Mouse Club," which ran for five years and featured a cast that included stars such as Britney Spears, Christina Aguilera, Justin Timberlake, Keri Russell and Ryan Gosling.)

The frustration is even higher for Day's family and friends, says Adkins, 75, who last saw her brother when she visited in the summer of 2017, when he seemed fine although he was taking care of the ailing Caswell.

"He was alert, he was healthy, he was fine," Adkins said. "(Police) are trying to portray him as a reclusive, demented person but in one year's time you can't become that way. My mother died of Alzheimer's, I know the process. When you're taking care of someone, you don't visit, you don't go out, so, yes, you're 'reclusive.'"

She said Day and Caswell worked for the producers of the Renaissance Pleasure Faires and Dickens Christmas Fairs from the late 1960s into the 1980s. She said they moved to Oregon in the mid-1980s, and Day had a side business making and selling his own line of wine jellies.

She has many questions and suspicions about her brother's disappearance but nothing solid. So she is trying to spread the word about him through Facebook, a podcast called The Vanished and local media. She can't believe he would just disappear voluntarily.

"After Ernie fell, they called an ambulance to take him to the hospital and that could have set my brother off," she said. "He could have committed suicide. And Oregon is full of rivers.

"I wake up every morning with a prayer they will find him and let me know," she said. Meanwhile, "I'm trying to keep him on everybody's mind and spread the word as far as possible, in case somebody somewhere knows something."