luke shambrook was last seen leaving candlebark campground on friday .
the 11-year old was camping in the victorian national park with his family .
he has been missing for two nights and temperatures dipped to as low as eight degrees celsius on saturday night .
there has been an unconfirmed sighting of luke with police acting quickly .
the 11-year-old was reportedly seen walking 4 kms from his campsite .
luke has limited speech and his family says he is probably confused .
a large search is being carried by a medley of search and rescue teams .
police also said conditions are favourable for his survival overnight .
they have issued an extensive description of luke and his clothing .