The young woman's employer became alarmed when she did not turn up to work on Monday and called the police.
Firemen broke open the door to her studio apartment on the Wiedner Hauptstrasse on Tuesday evening, to find her half-naked body lying face down on a mattress on the floor.
Detectives said that an autopsy showed she had no external injuries, and have now ordered a toxicological report to see if she was poisoned. Police spokesman Thomas Keiblinger said that traces of blood were found near her head, which may indicate an internal injury.
A forensics team initially had trouble examining the scene as all the light bulbs in her apartment had burnt out and had to be replaced with the help of a ladder.
Keiblinger said the young woman was from Colorado and had been studying and working in Vienna for around three years. Her employer said she was "very reliable" and had therefore thought it was unusual when she didn't turn up for work.
The Krone newspaper has named her as Lauren M., although this hasn't been confirmed by police.