Shaniesha Forbes, of East Flatbush, was last seen on Friday.
On Sunday, a passerby discovered her naked, burned and partially buried body in the sand in Gravesend.
"She didn't deserve this," sister Shanah Forbes said.
Shanah, 21, was the oldest of four girls. Now, she is the oldest of three girls.
The Forbes family is destroyed by the brutal discovery and could only beg for help, hoping someone will explain how or why such a thing could take place.
Shaniesha was the third of the four girls and a student at the Academy for Young Writers High School in East New York. Her mother was too heartbroken to speak, but Shanah said the family is determined to find out what happened.
The cause of death has not yet been determined.
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