Updated

James Yoblonski, a Wisconsin 13-year-old, has been missing for more than a month after police say he left home with a family car — and possibly his dad's handgun — in mid-June.

The younger Yoblonksi's last suspected whereabouts were near the Baraboo Bluffs on the western edge of Devil's Lake State Park on June 11, according to the Sauk County Sheriff's Office.

Now, his worried father is offering a $10,000 reward for his son's safe return.

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James Yoblonski inset over Devils Lake rock formation Devils Doorway

A photo of missing 13-year-old James Yoblonski provided by the Sauk County Sheriff's Office inset over the Devil's Doorway rock formation at Devil's Lake State Park in Wisconsin. (iStock, Sauk County Sheriff's Office)

And the money will come from mortgaging his home, William Yoblonski told the Madison-based WISC News.

"The $10,000 reward is only if he’s found," he told the local news station. "In the last three weeks, we haven’t gotten any tips or anything."

James ran away last month, likely to live off the grid at Devil's Lake State Park, Madison.com reported at the time.

During a large-scale search effort, police dogs found a possible campsite but no other signs of the boy.

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As the search continues, his father has raised concerns that the boy may have been picked up by someone.

"As much as they searched, they should have found some evidence of him being in there, and they found nothing," he told WISC.

The 360-acre lake lies below quartzite bluffs as tall as 500 feet, according to the state's Department of Natural Resources.

Map of Devil's Lake State Park (Mobile users go here)

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The park contains hundreds of campsites and a handful of showers, restrooms and outhouses. Drinking water is available at dozens of taps placed throughout the park. 

Anyone with information on James' whereabouts is asked to call the Sauk County Sheriff's Office at 608-355-4495.