Search for 9-year-old girl who vanished on a New York camping trip enters critical stage

The family of Charlotte Sena, who went missing Saturday evening in upstate New York, is asking the public for help as authorities ramp up their search for the 9-year-old they fear could have been abducted.

Charlotte, who was camping in Moreau Lake State Park with her family, went on a bike ride with close friends around dinner time and never returned, officials said.

Police believe Charlotte could be in "imminent danger," according to an Amber Alert issued Sunday morning.

"Following our exhaustive search of the park we took that step of issuing the Amber Alert because we felt that that exhaustive search, when we couldn't find her here, it was quite possible that an abduction had taken place," said Lt. Colonel Richard Mazzone of the Uniform Force of the State Police.

When she disappeared, Charlotte was wearing an orange tie-dyed Pokémon shirt, dark blue pants, black Crocs and a gray bike helmet, according to a description provided by state police.

The number of people searching for Charlotte has grown to 400 people, state police said. They come from 34 volunteer fire departments and private groups as well as federal, state and local law enforcement.

The search area has expanded over 46 linear miles, authorities said.

"This is a critical time. The statistics tell us in possible abductions, which this well may be, that first 24 to 48 hours is critical," CNN Chief Law Enforcement and Intelligence Analyst John Miller said on CNN This Morning.

Charlotte's family is now asking the public for information that could help bring her home.

"No tip is insignificant," Jené Sena, Charlotte's aunt, told CNN affiliate WCBS. "She is a blonde, adorable 9-year-old little girl with bangs. She has green eyes, just under 5 feet tall and she is just a sweet, adorable girl."

Charlotte was last seen around 6:15 p.m. Saturday, riding her bike in one of the park's loops. She had done a few loops with friends and wanted to do one more by herself, New York Gov. Kathy Hochul said at a news conference. Her mother reported her missing around 6:45 p.m., after Charlotte's bike was found in the loop without her, Mazzone said.

"Once they found her bike during that search, they realized she's not on it, she hasn't gone too far, she didn't get lost. Something's really wrong," Miller said.

"We just want her returned safely like any parent would. No tip is too small, please call if you know anything at all," reads a statement from Charlotte's family provided to NBC News and other outlets.

The state park, roughly 45 miles north of Albany, is more than 4,600 acres and "lies amid hardwood forests, pine stands and rocky ridges," according to the Department of Environmental Conservation.

"They're using just about every resource you can think of - helicopters, thermal imaging, license plate readers, video - to the extent that it's available in that park," Miller said. "They have some of that technology in the area, but it's not like had this happened in Albany or New York City."

"We are leaving no stone, no branch, no table, no cabin unturned, untouched, unexamined in our search to find Charlotte," Hochul said. "If you know anything, if you've seen anything, if you hear anything, please contact 911 to tell us what you know."

Moreau Lake State Park said in a Facebook post it is closed until further notice.

CNN's Jared Formanek and Christina Maxouris contributed to this report.