The crime was caught on surveillance tape and authorities are hoping someone will recognize the suspects.
The incident occurred on the 1300 block of East Ridge Pike around 8:50 a.m. Thursday.
The 84-year-old man was sitting in his real estate office when he buzzed in the two suspects into his secure building under the guise they wanted to rent an apartment.
Police say after telling them he didn't have one available, they pulled out a handgun and announced a holdup.
One of the suspects tied him up to his chair as another rifled through his pockets to steal all his cash, the video shows.
They then ripped the phone off his desk and threw it across the room before leaving.
Tenants and neighbors were disturbed and upset that someone would terrify an 84-year-old man in his office for his cash.
The sex of one of the suspects is unknown because of the heavy clothing they were wearing and the face was covered up by what appears to be a burka.
The other suspect is clearly visible and made no attempt to cover his face.
Fortunately, the 84-year-man was not injured, but shaken up pretty badly.
If you recognize the man that was clearly visible, you're being asked to call Plymouth Township Police.