ON THE NORTH SHORE — Advertising experts say billboards are most effective when delivering a simple, direct message. "Missing dog. Rowdi,'' is one example, especially when accompanied by an image of a large yellow Labrador with a warm nose and dark eyes that say, "I want to go home.''

Such a billboard appears not far from Lake Superior, along Hwy. 61, headed south from Grand Marais.

Admittedly, passersby driving to the Twin Cities or other destinations from resorts along the Gunflint Trail or paddling trips into the Boundary Waters Canoe Area Wilderness (BWCAW) can't tell if the dog on the billboard has a warm or cold nose, or whether the big Labrador's eyes are saying anything at all.

But for dog lovers, it's difficult to interpret the image any other way.

Rowdi is one of thousands of dogs that go missing every year. How many of these animals are never heard from again is unknown. But enough are found, sometimes after days, weeks, months or even years, to keep Rowdi's family — Cory, Becky and 5-year-old Lily Carlson of Minneapolis — looking for their buddy.

Even now, 239 days after the 10-year-old Lab disappeared.

"On Feb. 10, my wife, daughter and I took a trip to Tofte to get away for a few days,'' Cory said. "It was about 9:30 at night and I let Rowdi out the door of the condo where we were staying before we went to bed. I watched him through a window. But the window was frosted and I lost sight of him. So I opened the door and called to him. But he was gone.''

Most of these situations end happily. The missing dog steps from behind a tree or a bush, wags a tail and returns quickly to a favorite couch or bed, happy enough to begin a long winter-night's snooze.

Not Rowdi.

"He didn't come when I called or when I went outside to look for him,'' Cory said. "We called the sheriff, and a deputy was there pretty quickly. But all we could find were Rowdi's tracks in the snow, heading toward, and crossing, Hwy. 61.''

In the months since, the Carlsons have posted fliers at trailheads with Rowdi's picture and a phone number (612-669-8488) to call. In addition to renting the billboard, they've searched with an airplane, employed a drone, paid for a direct mail campaign and have a Facebook page, where they've accepted about $13,000 in donations to help fund a search that so far has cost more than $20,000.

They've also placed trail cameras in the woods along the North Shore.

"We've seen deer, other dogs and bobcats on the cameras,'' Cory said. "And wolves. Lots of wolves.''

The Carlsons acknowledge that whatever inspired Rowdi to go wandering on that fateful night, his journey might have ended in a deadly encounter with a wolf.

But maybe not.

Maybe, they say, Rowdi is still wandering among the pines, birches and aspens in northeast Minnesota. Or maybe he was picked up by a good Samaritan who thought he had been dumped off by a callous owner.

"Maybe that good Samaritan is keeping Rowdi, thinking he's a stray,'' Cory said. "It's happened with other dogs.''

So it has, says Amy Addy of Duluth, a volunteer with The Retrievers, a Minneapolis-based group that helps locate lost dogs, citing the case of Zoey, a toy poodle found after she disappeared from her White Bear Lake home, only to be located 17 months later in Hinckley, Minn.

Other dogs have been found after even longer absences. A golden retriever named Murphy disappeared in California while his family was camping, only to be located two years later, five miles from where he went missing.

Abby, a black Labrador mix, was gone from her Pennsylvania home even longer — 10 years — before she showed up on the porch of a home 10 miles from where she was last seen.

Cory said he and his family have had considerable support from people along the North Shore in their search for Rowdi. But they've also experienced pushback from some people who say they should accept that Rowdi is never coming home.

"We've had some of our posters torn down at trailheads and a few phone calls from people who say we're wasting our time, that Rowdi is dead and it's time to move on,'' Cory said. "At this point, in some ways, it would be easier to give up. It's almost like a part-time job, responding to people and keeping up with social media and traveling Up North. But I've come across so many stories of lost dogs that have been found, the possibility of him being found is enough for me.''

Acquiring Rowdi as a pup was Becky Carlson's idea. Cory had experienced an abusive childhood, he said, and her recommendation to him to see a therapist and buy a dog proved correct on both counts.

"When we picked him out of the litter, he seemed like the one I connected with most,'' Cory said. "He was a typical puppy. He chewed stuff and he loved to run. I couldn't run fast enough alongside him, so I got a bike. And he was definitely a retriever. I'd throw tennis balls into the Mississippi and he'd love to retrieve them. My wife is a runner and even as a 10-year-old he'd run three miles with her.''

The search for Rowdi will continue indefinitely, Cory said, who said he owes it to the dog that has given so much to him and his family.

But the Carlsons also are turning a page. At the end of the month, they'll pick up a new puppy, who will be a friend to them and, they say, to Rowdi when he comes home.

"People can hold different emotions at the same time,'' Cory said. "I remain saddened about Rowdi's disappearance, yet I'm grateful and excited about the new dog.''