Surveillance video shows the suspects entering the Diaz Grocery store on the 1100 block of South 54th Street back on October 11.
Click here to watch the surveillance video
One of the thieves broke the plexiglass door leading to the register area, then struck the 64-year-old clerk in the face with a gun.
The group then can be seen grabbing handfuls of cash from the register and going through the victim's pockets.
Another suspect forced a customer at gunpoint to the rear of the store, where he stole the man's wallet.
The suspects then fled the scene in an unknown direction.
Police describe the suspects as four black males wearing hooded sweatshirts or jackets with masks over their faces.
Anyone with information is asked to call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).
You can also submit an anonymous tip online at PhillyPolice.com.