How could that possibly be true? If true, it's got to be the handy work of former Gov. Sarah Palin?
Alaska is more willing to let hitchhikers catch a ride (in many states, it's illegal); however, that's a far cry from requiring citizens to serve as a taxi driver for a non-paying complete stranger who could be looking to rob, rape, or kill his driver. NO. This is not true.
Now it may be true (though found no law suggesting such) that you are required to call for help if you see a stranded motorist or distressed pedestrian, but I seriously doubt the law imposes any criminal liability for failing to do so.