Police told CBS affiliate WKMG that the search is focused on a wooded area because Nadia's bicycle was discovered at the end of a cul-de-sac on her street about a half mile away from her home.
Authorities said they have been working the case as a search-and-rescue case and as a possible abduction.
"Until we get something that tells us otherwise, we're not going to give up," Winter Springs police Chief Kevin Brunelle told the Orlando Sentinel. "When it comes to the well-being of another human being, we're not going to establish a timeline."
More than 100 searchers were looking for Nadia Sunday night using ATVs, amphibious vehicles and side scan sonar machines. Thirty search-dog teams were also out in the woods.
Police described Bloom as white, about 5-feet tall and 85 pounds. She has brown hair and brown eyes and was last seen wearing an orange T-shirt and blue shorts. She was carrying a black backpack with a horse on it.
Police said the girl has autism and does not have her required medication with her.
Winter Springs is about 15 miles north of Orlando.
Please contact the Florida Department of Law Enforcement Tip Line at 1-866-282-0672 with any information on Nadia's disappearance.