Vigilantism isn't even allowed in superhero movies and for a reason. There is a severe risk in people taking justice into their own hands. Especially gang members.
For instance, they won't have the burden of proof nor are they educated to find them. Their aggression can be misplaced by a manipulator who would use them to punish his own enemy. Not an actual scammer. If people can scam someone, they can also be fake scammed by someone.
And make no mistake, there would have to be violence. There is no gang without it.
Yes scamming someone is bad and unjustifiable, but it's also an injustice to have someone go to a cosy prison (Scandinavian countries' MO) for a murder, while the scammers would probably get beaten to near death by the gang members. As bad as scamming innocents is - it's not as bad as murder. So this would be effective but immoral on this level of consequences. It would also set a terrible precedent for people taking justice into their own hands for all matters they are disatisfied.
I wouldn't expect gang members to reserve their actions to scamming only, once they've felt the power. It would be legalizing or decriminalizing racqueteering through the backdoor.
I think the police lets the gang members threaten each other in hopes that they'll escalate reduce each other's numbers. Making their jobs easier.
Better to use the TikTok clout into shaming the police into catching the scammers. Something like this but more aggressive and on a larger scale.