The vessel, which was under tow at the time of its disappearance and was unmanned, was bound for Burma, where Pandaw has run a successful river cruising operation since 1995,
The three-year-old vessel was originally reported by the tug operators to "have capsized in heavy seas after the hull became swamped". However, the owners now believe the boat to have been stolen, possibly to be stripped of its luxury fittings and then broken up to supply the lucrative East Asian market for scrap metal.
In an appeal to maritime and travel industry contacts, Pandaw founder Paul Strachan wrote: "I expect you will have heard rumours that the Saigon was stolen in an act of piracy rather than sunk. I cannot comment. But we have offered a reward for any information that might lead to its recovery. Please pass the reward notice to any contacts you might have, particularly in Indonesia. Meanwhile, we have investigators working on the ground."
The four-deck Saigon, which is 50 metres long and 10 metres wide, was reported lost off the Malaysian coast on December 21.
Launched by Strachan, a Burma scholar and publisher in the early 1990s, Pandaw originally traded as the Irrawaddy Flotilla Company (IFC), a revival of the Burmese riverboat service that flourished in British-ruled Burma between the 1860s and 1940s. Managed by Glasgow's P Henderson & Co, the IFC was the largest fleet of river boats in the world in the 1920s, with more than 600 vessels carrying nine million passengers a year.
Its successor, Pandaw, runs cruises on four routes on the Irrawaddy in Burma and four on the Mekong in Vietnam and Cambodia. Pandaw, which has two new ships under construction, described the loss as "a setback, but one that doesn't affect our growth plans at all".