Police say the person is a heavyset, white male in his 20s or 30s who stands 5-foot-7 or 5-8.
They say he is balding or has a short haircut and has tattoos on his chest and arms.
They say the man was seen speaking with several women along the beach.
Police would also like to talk to anyone who may have talked to the victim – 17-year-old Anna-Rose Shove of Lanson Road.
She was last seen wearing a pink and white two-piece swim suit.
Shove was found in Lake Ontario on Sunday.
Campers at Brennan's Beach in the town of Richland pulled the teenager's body from the lake and contacted 911.
She was pronounced dead at the scene around 4:25 p.m.
Anyone who has any information or may have seen Shove at Brennan's Beach should contact State Police Investigators in Pulaski at (315) 298-1470.
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