Police used a helicopter to scour the area around Lake Zug on Tuesday in a bid to find Olivia Ostergaard, who failed to return to her apartment in the city of Zug last week.
They have used dog tracking teams and boats to search around the lake and the Ägeri Lake but the Neue Zuger Zeitung newspaper reported on Wednesday that investigators failed to seek what could be crucial evidence.
The newspaper said officers failed to check surveillance camera videos at the Zug train station.
At least, they did not check the videos quickly enough.
The videotape is automatically erased after 72 hours and by the time Zug police got around to viewing it, it was already too late, the Neue Zuger Zeitung reported.
Police spokesman Marcel Schlatter confirmed that the police did not put their request to view the surveillance video at the right time.
A spokesman from Swiss Federal Railways said if police had sought the relevant videotape earlier it would have been recorded.
The Zug train station has no less than 25 surveillance cameras installed inside the train station and overlooking the platforms.
Zug police said Ostergaard was last seen at 5.30am on March 26th, when she probably left for the University of Zurich but never arrived.
The boyfriend of Ostergaard sounded the alert last Tuesday when she failed to return to the apartment they shared in Zug.
Her 15- and 17-year-old brothers launched a Facebook page called, in German, “Where’s Olivia?” that already has more than 9,500 followers and Danish journalists have travelled to Switzerland to follow the story.
Her friends were planning to start a private search on Wednesday in a bid to find the girl themselves.
According to the police description, Ostergaard is 178 centimetres tall, of a slim build, with long blond hair.
She was believed to be wearing a black coat with a hood and a dark dress.
Police said she has three tattoos, one each on the forearms and on the right thumb.