18-year-old Harsha Maddula, Northwestern pre-med sophomore and straight-A student, disappeared on last Saturday after attending an off-campus party with friends.

A fisherman found Maddula's body floating between two boats near the Sheridan Road Bridge at the harbour in Wilmette on Thursday night, according to ABC News affiliate WLS-TV.

Maddula's wallet, Northwestern identification card and his cellphone were found in his pockets, according to Northwestern University spokesman Alan Cubbage.

"Wilmette Police investigators on the scene said there were no signs of foul play on the body," Cubbage said in a news conference on Thursday night.

The cause of death is under investigation.

"On behalf of Northwestern University, I extend our deepest sympathies to Harsha's family and to his many friends at Northwestern," university president Morton Schapiro said.

"Our hearts and thoughts are with them. The loss of one member of the Northwestern community deeply affects us all."

Earlier, divers searched the Lake Michigan harbor for hours but failed to find any signs of Maddula.

The search included 21 law enforcement agencies and fire departments, hundreds of Northwestern students and the FBI.

Maddula's family flew from their home in Long Island, NY, to assist with the search, and put up a USD 25,000 reward for information on his whereabouts. They described Maddula as a bookworm not prone to adventures or partying.

The family said they wanted answers to explain his still-mysterious death.

"We really have no idea, no clue what could have happened to him," his cousin Srinu Maddula told ABC News.

Srinu said the family has little information about the party that his cousin was attending or what friends he was with on the night of his disappearance.