Officers say the man was attacked last November after listing a variety of items for sale on the website including some inexpensive costume jewelry.
Investigators say the assailant was likely responding to one of the ads and might have believed the jewelry was valuable, because the postings were unclear.
Const. Brian Montague says police are still looking for a suspect and have taken the unusual step of releasing the victim's photo to show the gravity of the beating.
The photo released Tuesday was taken shortly after the attack and shows the victim in hospital with his eyes swollen shut, severe head and facial injuries and tubes in his mouth.
Montague says the victim was beaten unconscious and several items were stolen from his home before he came to and knocked on a neighbour's door asking for help.
Investigators have identified a person of interest from surveillance footage that shows a man wearing dark clothing and a black DC brand baseball hat with a yellow logo and green brim.
Police are warning people to take caution when using Craigslist, by doing any exchanges in a public place if possible or bringing a friend when buying or selling somewhere private.