Ilya had been huddling near at outfall pipe at a Linden refinery last week to try to stay warm.
Marine mammal rescuers devised a plan to capture the sea cow and return it to Florida's warmer waters. However, no one has seen Ilya since Friday afternoon.
Bob Schoelkopf of the Marine Mammal Stranding Center says he hopes Ilya is heading south on his own.
Schoelkopf asks anyone who sees the manatee to call the stranding center at 609-266-0538 because Ilya may still need help.