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."
When asked if cops were involved in the chain-hunt, Sauce Diddy told us ... "Nobody's calling the police. We're gonna find it. We're gonna get it back."