A Hollywood celebrity, a teenage death in a bathroom and the Church of Scientology is a toxic brew for global gossipmongers and, sure enough, the death of John Travolta's 16-year-old son, Jett, has triggered an orgy of internet chatter. Some of the speculation is being driven in an organised way by critics of the Church of Scientology ("Co$" in internet parlance).

According to the Travolta family, Jett suffered from regular seizures (around one a week) and had been diagnosed with Kawasaki syndrome, a rare childhood condition with some life-threatening symptoms but rarely fatal. Details of Jett's death, in the bathroom of Travolta's holiday home in the Bahamas after a reported seizure, are sketchy. The postmortem results will almost certainly be kept private by Travolta and his wife, Kelly Preston.

For members of Anonymous, an online group of anti-Scientology activists, Jett's death is an opportunity to repeat old allegations against Travolta and Scientology: that Jett suffered a form of autism but Travolta and Preston, who are Scientologists, were in denial about it because it is claimed that Scientology argues that autism is psychosomatic and must not be managed with mainstream medication or psychiatry.

It is alleged online that Travolta and Scientology may have somehow prevented the treatment of Jett's condition and put him through "detox programmes" created by Scientology founder L Ron Hubbard. But in interviews Preston has described the "detox" only as being "90% organic" apart from "a little bit of junk food".

Travolta's lawyers, Michael Ossi and Michael McDermott, told the celebrity website TMZ.com that Jett took an anti-seizure drug called Depakote and it was only stopped on medical advice. The British branch of Scientology did not respond to questions about its position on autism.

"Scientologists use medical drugs when physically ill and also rely on the advice and treatment of medical doctors," said a spokesman.

The online speculation comes at a convenient moment for the anti-Scientology campaign, with worldwide protests planned this Saturday, but there may be a backlash if it is seen to be exploiting a private tragedy.

• This article was amended on Friday 9 January 2009. John Travolta's son died during a family holiday in the Bahamas, not in Barbados. This has been corrected.