State Police Sgt. Stephen Jones says three boats are being used, including one with side-scan sonar. Divers could be used, too.
Aircraft are also searching along banks of the Raritan River and area roads.
Police say 21-year-old Shamsid-Din Abdur-Raheem, of Galloway, told them Tuesday that he threw his daughter, Zara Malani-lin Abdur, off the Driscoll Bridge on the Garden State Parkway.
Abdur-Raheem is charged with attempted murder.
Police say Abdur-Raheem forced his way into the grandmother's East Orange apartment around 4 p.m. Tuesday, striking her in the face, choking her and pulling the baby from her arms before fleeing in a van.
The 60-year-old grandmother, whom police declined to identify, chased after Abdur-Raheem and was struck when she tried to stop him by throwing herself in the path of his vehicle, authorities said. Abdur-Raheem then headed toward southern New Jersey, and police say he told them he tossed the child from the Garden State Parkway's Driscoll Bridge, over the Raritan River, on his way.
The child's mother, Venetta Benjamin, had no visible reaction Thursday as she watched Abdur-Raheem, clad in an orange jail jumpsuit, answer questions on the video screen in court. She left the court, accompanied by a woman in a priest's collar and other relatives, without commenting.
Officials say Benjamin, who has sole custody of the infant, had sought a restraining order against Abdur-Raheem around the same time Tuesday afternoon that he is accused of showing up at her mother's East Orange apartment. Benjamin's lawyer, Mitchell Liebowitz, said the baby was snatched before the restraining order was served.
New Jersey's acting attorney general, Paula Dow, has classified the case as severe domestic violence.
Abdur-Raheem's father, Mushin Raheem, said the relationship between his son and Benjamin, who are not married, had been bumpy since they started dating as freshmen at The Richard Stockton College of New Jersey.
"They had their problems, you know what I mean?" Raheem said, saying his son could get angry but not unusually so.
"Everybody has a temper," he said. "He's mad, you get mad, you know."
Raheem said his son and Benjamin moved into an apartment together in Galloway Township about two weeks ago. She moved out within a week, Raheem said, going to live with her mother.
Raheem said that the couple had brought the baby to his home four or five times, and that the idea that his granddaughter could be dead was weighing heavily.
"Man, I'm distraught," he said. "I'm distraught."
Raheem said that Amin Muhammad, an Atlantic City imam who was close to his son, brought the young man to his father's home Tuesday night. Police arrested Raheem there later.
He wouldn't say what his son, who aspired to go into criminal law, told him then.
"It's very difficult," Raheem said. "Everybody in my family's hurt by this."
Amber Alert questions
Meanwhile, acting state Attorney General Paula Dow says she's investigating why an Amber Alert wasn't activated after police said Abdur-Raheem snatched the child from her grandmother in East Orange.
By the time officials were ready to issue an alert, he was already in custody.
