"Why yu[sic] have to leave us so soon shawn, yu was like another bro, yu got my bro in tears he will never find another person like yu," one Facebook user wrote on the page.
"What a nice boy Shawn was! Always, a respectful & hard working student," wrote another user. "He had the most infectious smile. He will be greatly missed. My heart goes out to all of his family and friends. I really hope that the relentless violence would one day, just stop!"
Plummer was shot once in the head on Seagirt Avenue and Beach 29th Street, just blocks away from him home just before 3 p.m. and was pronounced dead at St. John's Hospital.
No arrests have been made in connection to the incident and police have not named any suspects, they said.