The PC's will either be freelance detectives or working for a reputable agency. However, this is not essential. They could also be working for a newspaper. To name just one example.
The teenager ran away from an exclusive school because of racism on the part of his peers and teachers. Her parent’s ordered him to man up. Of course a willful ignorance of the full scope of the problem didn’t help matters.
He sent his sister a series of postcards from across the country, with postmarks of various monuments. She will give the characters these postcards if asked.
Checking with the police for leads will result in a visit from the Mayor’s personal staff, telling them to back off. Checking on the streets will bring in the local crime lord’s henchmen, also telling them to back off.
Someone will send the PCs a picture of the kid. Deceased. The house the boy was staying in, where the picture was taken, has been bulldozed and a new park is on the lot.
The investigation leads down the dark alleyways of the city and up the heights of power. Organized crime and the mayors office are in bed together and both sides are doing their utmost to obstruct the investigation.
The local papers are afraid to even print a hint of the story without solid evidence.
If the PCs press hard enough, the warnings will go to outright assassination attempts.
Editor's Note: The ending is left intentionally open for the GM to ultimately decide the direction in which to proceed. This is a short crime mini-campaign I was playing through with a friend last week via another chatroom. When I noticed the Freetext Friday challenge, I just thought it had to be posted.