Blac Chyna Zeroes in on Jealous Friends After Safe Heist

Blac Chyna is adamant friends-turned-haters are behind her $200k home burglary, and she's out to nab 'em ... TMZ has learned.

Sources connected to BC and Rob Kardashian tell us she thinks the heist was done by an inner circle friend who's bitter about her new lifestyle -- no booze and no cigs. BC used to be down to party on the reg, but she's been sober for several months.

She also thinks the culprit is jealous of her $325k engagement rock.

We broke the story ... the burglar(s) made off with cash and jewelry from Chyna's safe. We're told very few people even knew about the safe -- another reason she's convinced it was an inside job.