Arensen was last seen at Hillcrest Christian Church in the 17500 block of Rinaldi Street in the Grenada Hills neighborhood of Los Angeles, California at 7:30 a.m. on Sunday, August 25, 1968. She left home to prepare a church bulletin and has never been heard from again.

Arensen's blue car was found parked outside the church at 9:15 a.m. Her keys were in the church office, her eyeglasses were on the office floor, and the electric typewriter was running. There no indications of a struggle. Arensen's olive-brown 14-inch-long envelope style purse disappeared with her. There has been no activity on her checking account since her disappearance, and her passport was left behind. She would not have been able to see well without her glasses.

Arensen got married only two months before she disappeared and resided with her husband in the 10800 block of Zelzah Avenue in Los Angeles. Her husband was an associate youth minister at the church. She did not normally prepare church bulletins on Sundays, but on Thursdays and Fridays. Arensen's father theorized that someone followed her to the church office and attacked her there. No suspects have ever been named in her disappearance, and her case remains unsolved.