This comes one day after the 13-year-old girl who disappeared along with them was rescued from the home of a man later charged with kidnapping.
Sarah Maynard was found in 30-year-old Matthew Hoffman's basement, four days after she and her family disappeared from their home in Howard.
Police said they still want to remain optimistic that 32-year-old Tina Herrmann, her 10-year-old son, Kody, and Herrmann's friend, 41-year-old Stephanie Sprang, are alive.
Hermann's home was found littered with beer cans and a significant amount blood. DNA was expected to begin Monday.
The girl was hospitalized and is reported in good condition, but police did not reveal any other details.
Authorities believe that the teen was "under the control" of Hoffman since she went missing. Police do not know if Hoffman is connected to the family.
Police closed off Foundation Park after an officer patrolling the area found items possibly related to Maynard and the others overnight.
Those items turned out to be unrelated to the case, so authorities reopened the park at midmorning.
However, they roped off the park yet again. This time, investigators honed in on the lake within the park - using a boat equipped with sonar to conduct their search.
Search crews surfaced an old four-door car out of the lake and an SUV a short time later. Investigators said it didn't appear that either vehicle was related to the people's disappearances.
About 200 community members gathered Monday evening for a candlelight vigil at a church about two blocks from Hoffman's home and around the corner from the park.
Hoffman was held without bail over the weekend. Authorities have described him as uncooperative.
The Associated Press contributed to this report.