Sarai Sierra, 33, was last in touch her family on Jan. 21, the day she was supposed to fly home after two weeks in Turkey.
A police official said authorities were reviewing footage from around Istanbul's Taksim neighborhood - the city's main hub where she was staying at a hostel.
Several police teams have also been dispatched to surrounding neighborhoods to find possible clues and witnesses, the official said. He spoke on condition of anonymity, in line with government rules that bar civil servants from speaking to reporters without prior authorization.
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 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 Associated Press Sunday.
Sierra had planned to go on the trip with a friend but ended up going by herself when the friend couldn't make it. She was looking forward to exploring her hobby of photography, her family said.
Crime in Turkey is generally low and Istanbul is a relatively safe city for travelers, though there are areas where women would be advised to avoid going alone at night. The Galata and the nearby Galata Bridge areas have been gentrified and are home to fish restaurants, chic cafes and boutiques.