48-year-old Jonathan Rivers was brutally assaulted at the Buena Vista Houses on Riverdale Avenue.
The security guard was trying to break up a crowd of party goers in the courtyard of a building when several people attacked him.
Police say one of the attackers hit the guard in the face with a rock.
Rivers suffered injuries to his face that forced doctors to remove one of his eyes on Wednesday.
Police are searching for the suspects and they are trying to enhance security video from the building that may show some or all of the attack.
If you have information that might help investigators call the Yonkers Police Detective Division at 914-377-7724.
The victim's company, Force One Security, is offering a $1,000 reward for any information that leads to his arrest.