The sister of a 21-year-old woman who went missing in Tokyo nearly two weeks ago is working with the British Embassy and the Japanese police in an attempt to locate her sibling.

Lucie Blackman, a former British Airways flight attendant from the town of Sevenoaks in Kent, arrived in Japan with a friend in May on a tourist visa. Blackman and Louise Phillips, also 21, were working in the Casablanca hostess club in Tokyo’s Roppongi entertainment district until Blackman disappeared on July 1 after telling Phillips that she was going for a drive to a beach with a client.

Phillips later reportedly received a phone call from a man speaking in broken English who told her she would never see her friend again.

The man said he was holding Blackman, adding, “This is the last time you are going to hear about Lucie. This is goodbye.”

The caller also claimed that Lucie was starting a new life with him, that she had lots of “debts” and that he was going to force her to pay them off.

Toshihiko Mii, deputy superintendent at Azabu police station, which is handling the investigation, said they are keeping an open mind and treating the case as both a missing person inquiry and a potential kidnapping. As of Tuesday, however, the staff at the Casablanca club had not been interviewed by the police concerning Blackman’s disappearance.

Police are looking into the claim that the man also said Blackman was in Chiba Prefecture and that she was going to join his “newly risen religion.”

Sue Kinoshita, press officer at the British Embassy, said reports of Blackman being kidnapped by members of a cult or forced into prostitution are “pure speculation.”

The missing woman’s sister, 19-year-old Sophie Blackman, arrived in Japan late last week and has made appeals in the Japanese media for anyone with information to come forward.

“We don’t know where Lucie has gone or who she is with,” she was quoted as saying. “She would know a dangerous situation and avoid it at all costs.

“She is very intelligent and streetwise. She would not just go anywhere with anyone. But we just don’t know whether she is being held against her will or not, and we don’t know whether this call was a hoax or not.”

The British Embassy has set up a dedicated hot line (090-8591-0070) that anyone with information about Lucie Blackman can call in confidence. She is 172 cm tall and has shoulder-length blond hair and blue eyes. She was reportedly carrying a black bag and wearing a black dress and a necklace with a heart-shaped diamond on the day she disappeared.