Mrs Hagen is married to Tom Hagen, a businessman with an estimated fortune of 1.7bn Norwegian krone (€174m; £156m) made in the real estate and energy industries.
Detectives had been investigating the case discreetly for several weeks but decided to make it public on Wednesday in the hope that someone would come forward with information.
The wife of one of Norway's wealthiest businessmen has been kidnapped by a person or persons demanding a ransom of 9 million euros paid in Monero, the most popular privacy cryptocurrency, according to several local news outlets. Police had urged the family not to pay any ransom.
"There's no doubt that for the family, Anne-Elisabeth's kidnapping is a disgusting and inhumane act", he said, expressing hopes that news of her disappearance would lead to some kind of sign that she is alive.
It has also been reported that there had been limited contact between police and the suspects with the only communication sent through encrypted digital platforms.
The real estate investor owns 70% of the electricity company Elkraft, which he co-founded in 1992, Norwegian media reported.
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When paramedics arrived on the scene, they found carriages from both trains tilting half off the track. Masha said police had opened an inquest docket to investigate the cause of the collision.
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The paper also claimed the note said she would be killed if police became involved. The family made a decision to follow the police advice'.
"As in all serious criminal cases, time is an important factor, and we rely on tips.to help us find the missing woman".
'Our main theory is that the victim was kidnapped by unidentified perpetrators at her home. Broeske declined to comment other than saying "the threats (in the note) were of a very serious character".
Norwegian broadcaster NRK says the couple live a "secluded lifestyle" and asked the public to get in contact if any suspicious activity was seen in woodland that surround the family home.
Police inspector Tommy Brøske at a press conference in Lillestrom on Wednesday.
Such events are extremely rare in the Scandinavian country, which enjoys a generally low crime rate.