Turkish police are scanning security camera footage as they attempt to trace a tourist from New York City who went missing a week ago.
Sarai Sierra arrived on her own in Istanbul for a two-week holiday on January 7.
The 33-year-old had planned to go on the trip with a friend but ended up going by herself when the friend could not make it.
The mother-of-two was supposed to return to the US on January 21 but was not on her flight home and has not been heard from since.
Turkish authorities are reviewing CCTV pictures from around the hostel and neighbourhood she was staying in.
Mrs Sierra's passport and medical cards were still in her room.
No trace of her has been detected since last Monday, officials said.
Her brother David Jimenez and her husband, Steven Diaz-Sierra, set off for Istanbul at the weekend to help in the search.
"I don't want to come home without my sister," Mr Jimenez said as he left.
Just before she went missing, Mrs Sierrra told relatives how she planned to take photographs at the Galata Bridge, a well-known tourist destination that spans the Golden Horn waterway.
Her children, aged 11 and nine, do not know their mother is missing.
Her own mother Betzaida Jimenez said the situation has "been a nightmare".
"I'm forcing myself to get up because I have to get up," she said. "We're praying and trusting God that she's safe somewhere and we're going to find her."