Need Help With Wall of Shame Quest in Rejuvenation

[AwesomeDog45677]

It wouldn't let me choose Rejuvenation as a tag so I chose the option above it, sorry.

 

So I just watched the art piece get robbed and walked outside the museum and the dude said he was going to the black market. I looked around the area, but can't find him. Anyone know where to go? 

[Lillietea]

Do the Missing Children quest (can be picked up in the Help Center of the Central Building once it's open after a certain point in the story), it gives you access to the needed location.