Steve Francis -- Rappers Vow to Get Chain Back ... From 'Stupid Ass' Thief

Steve Francis can rest easy about his missing chain -- 'cause the rappers who were performing on the night he got jacked tell TMZ Sports they're on MISSION to get the necklace back to the NBA star.

We broke the story ... Francis was on the stage at a Sauce Twinz concert in Houston this weekend when some guy snatched the chain right off his neck.

Now Sauce Diddy -- who manages the Sauce Twinz (and was wearing the red backpack at the concert) -- tells us the guys feel terrible that it happened at their show ... and want to do everything in their power to make it right.

"Steve is good people," Sauce Diddy tells us ... "He's going to get his chain back. I'm going to make sure of it. One way or another."

Diddy is adamant the crook is NOT affiliated with the Sauce Twinz -- he's just a "random stupid ass" -- but says Steve didn't exactly do the best job of protecting himself that night.

"He must have been drunk. He was mumbling on the mic and bumping into people. At one point, one of my artists tried to get Steve to leave the stage."