Detectives from the LAPD are working around the clock to track down PnB Rock‘s killer, even alerting local pawn shops to keep an eye out for the jewelry stolen off the rapper’s neck.

Law enforcement sources tell TMZ … investigators are confident they’ll make an arrest, and have spoken with those close to PnB to determine exactly what type of jewelry he was wearing at the time of his murder.

We’re told investigators contacted numerous pawn shops in the area, asking them to alert cops if anyone tries to make a buck off the stolen pieces. The theory is that the murderer would want to get rid of the jewelry quick … otherwise, it would directly link him to the crime.

Our sources say detectives believe the suspect targeted PnB because of social media posts. The rapper shared a video of himself wearing several expensive chains, and his girlfriend, Steph Sibounheuang, shared their location just before the shooting.

What’s more, we’re told the entire crime was captured on surveillance … though sources inside the restaurant tell us that footage is blurry. Cops have been canvassing the area for other cameras, and are working to identify a possible getaway vehicle.

Our law enforcement sources say the killer was wearing a mask at the time of the shooting.