Mya Lyons was visiting her father for the summer when she was killed. Lyons' father found her lying in an alley about a half-block from his home in the 8400-block of South Gilbert Court.
Police did question a person of interest but later ruled the man out as a suspect.
The Lyons family gathered Wednesday evening for a news conference in the hopes of keeping pressure on police to find the girl's killer.
"If you have any conscience, if you have at least a little bit of heart left, turn yourself in because you will be caught," said Mya Lyons' mother, Ericka Barnes.
Family members also released balloons in Mya Lyons' memory.