It happened on December 24 around 4 p.m. at the 7-Eleven located on the 2900 block of Cottman Avenue.
Police say the victim agreed to meet there with an unknown man who had responded to his Craigslist ad to sell his MacBook laptop.
When he arrived, he entered the store and asked an employee if anyone was there to buy the laptop.
That's when the suspect was caught on camera walking into the store and punching the man from behind, knocking him to the ground.
The thief then grabbed the laptop, valued at $2,500, and took off in an unknown direction.
The suspect is described as a black male, 20 years-old, 6'3" tall with a thin build. He was wearing a black hooded sweatshirt, black pants and black shoes.
If you recognize this suspect, call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).
VIDEO: Click here to watch the surveillance video