Police would not say whether Johansen was acquainted with the man suspected of her murder.
“We are in the early stages of our preliminary investigation and cannot comment,” said police spokesman Thomas Fuxborg.
Johansen left the home she shared with her live-in boyfriend without her wallet, mobile phone, or keys between 7pm and 8pm on Thursday.
The 20-year-old, who is described as very organized, has not shown up for work. Nor has she contacted any relatives or acquaintances.
Police in Alingsås continued the search for Johansen on Monday and are calling on members of the public to come forward with any tips relating to her disappearance.