Turkey's private Dogan news agency meanwhile, reported that police had established that Sierra had traveled to Amsterdam, Netherlands, from Istanbul on Jan. 15 and then journeyed on to Munich, Germany, on Jan. 16, before returning to Istanbul on Jan. 19. Police were trying to determine the reason for her visit to the European cities, the report said.
Police were also trying to find the identity of a person she had been chatting with on the Internet, Dogan reported.
Another police official, contacted by The Associated Press, confirmed that Sierra had made a brief trip to Europe, but refused to provide further details. He also spoke on condition of anonymity saying he was not authorized to speak publicly about the investigation.
Before she went missing, the mother-of-two told family members that she planned to take some photographs at Galata Bridge, a well-known tourist destination about 2 kilometers (1.2 miles) away from Taksim that spans the Golden Horn waterway. She was then supposed to begin traveling home and was scheduled to arrive in New York City on Tuesday afternoon.
Her belongings, including her passport and phone, were found in her room. The first police official said authorities were therefore not able to track her by her cell phone.
Sierra's husband and brother were traveling to Istanbul to follow the search. Her two children, aged 11 and 9, do not know their mother is missing, her brother David Jimenez told the AP Sunday.