John McLaughlin, a 52-year-old American citizen, arrived in Oslo in late January and planned to travel from one end of Norway to the other, both on skis and by bus.

His family in Colorado has told police they received a postcard from him that was sent from Lillehammer in early February. Since then, they've heard nothing from him.

McLaughlin was due to return to the US on March 14. When he failed to do so, his family contacted the police.

"We have few leads," said Per Olav Utgaard of the Oslo Police District, adding that any tips from the public would be welcome.

Investigators are checking all the lodging accommodations along his planned route, in the hopes of tracking him down. McLaughlin, who has set off on extensive trips before, was said to be in good shape physically.

"We have tried following any electronic tracks he may have made (from a mobile phone or credit card, for example), but he has left few or none," said Utgaard.

A police press release described McLaughlin as being 182cm tall, weighing 80 kilos and having little hair. Police asked that any tips on McLaughlin's whereabout be called in to (+47) 22 66 90 50 or to the officers on duty at (+47) 22 66 99 66.