Lt. Fabian Pacheco said Friday that investigators working on Isabel Mercedes Celis' disappearance spent the night combing through the lake at a local park with sonar equipment.
He says they were acting on a tip, but he wouldn't elaborate. Officers also searched bodies of water in other city parks.
Pacheco says police are also looking for anyone who took video during a baseball game that Isabel's family attended the night before she disappeared.
Police are also now looking for a group of people who may have been walking in the area last Saturday between 1 and 1:30 a.m. Authorities say the group, which includes two males and three females, may be potential witnesses or have information useful to the investigation.
Isabel's parents say they last saw the first-grader in her bedroom April 20, and they awoke the next morning to find her missing. Police say a window was open with the screen pushed aside.