last signal was received from their tracker device high above the adriatic sea. there were thunderstorms in the a a m pil since then, silence. >> they've been flying for four days. in four days or 100 hours is right about the limitations of flying a gas balloon that size. >> boats and planes launched from italy and searched till sundown. nothing. on board they have a satellite phone, a radio, cell phones but they're not answering. an emergency beacon should activate when it hits water. nothing. they have survival suits, life jackets and two small life rafts. >> hopefully they are floating around in their rafts. just an incredible amount of support from all over the country. people calling, e-mailing, praying. >> reporter: the search continues. still no sign of these intrepid adventurers. nick watt, abc news, london. right after we do this next