The Federal Bureau of Investigation is involved in the search for a missing Tennessee toddler who authorities say was last seen in December.

Evelyn Boswell, a 15-month-old girl from Blountville, wasn't reported missing by her family until Feb. 18. The Tennessee Bureau of Investigation issued an Amber Alert the next day at the request of the Sullivan County Sheriff's Office.

"This is unlike anything I have ever seen,” said Sullivan County Sheriff Jeff Cassidy, explaining the complicated nature of a case in which investigators have received conflicting and inaccurate information.

TBI spokeswoman Leslie Earhart said that the FBI has been assisting TBI and Sullivan County in the investigation since the Amber Alert was issued Feb. 19.

The investigation spans two states.

William McCloud, 33, and Angela Boswell, 42, who is the missing girl's grandmother, were arrested Friday on fugitive warrants in North Carolina. The pair will be extradited back to Tennessee, said Lt. Logan Kerr, a spokesman for the Wilkes County Sheriff's Office in North Carolina.

Angela Boswell and McCloud are charged with driving a stolen car that authorities previously said was connected with Evelyn's case.

Law enforcement said the missing girl's mother was involved in a botched car sale that allegedly eventually became vehicle theft.

Boswell's grandfather was ultimately the one who reported her missing, telling the Department of Children's Services that certain family members hadn't seen her in two months.

The case was referred to the Sullivan County Sheriff's Office, launching an investigation.

In an interview with WCYB News 5, the girl’s mother claimed she was afraid to report her daughter missing, and said Evelyn is with a babysitter. She would not identify the sitter.

“The reason I didn’t report it or anything was I knew the person who had her, and I didn’t want them to run away with her,” Megan "Maggie: Boswell told reporters. “And as soon as they thought anything was going on, they just kinda vanished. So I’m just kinda worried, you know, about where they are at. What they’re doing with her."

Reward reaches $56K as authorities caution against mysterious GoFundMe

As of Monday, a reward totaling $56,000 has been offered for information leading to Evelyn's safe return. Cassidy himself put $1,000 toward it, along with several local businesses and individuals.

Ballad Health has pledged $25,000 toward the reward pool, along with two individuals named Tommy Boswell Sr. and Tommy Boswell Jr. who have offered $10,000 each. It's unclear whether the two men have any relation to Evelyn's family.

But the sheriff's office on Sunday also cautioned against an online fundraising account apparently set up on its behalf, but with which the law enforcement agency is not affiliated.

"The Sullivan County Sheriff’s Office has not established a GoFundMe account and has not authorized anyone to establish one on its behalf," the department wrote on its Facebook page.

"We are aware of an account that someone has set up and an inquiry has been made to GoFundMe in reference to it."

On Monday, it did not appear the unauthorized fundraising effort was still active on GoFundMe.

It's unclear who was behind the page or whether the sheriff's office has received answers about it.

Officials received conflicting information on when toddler last seen

Law enforcement has said Evelyn, who is 2 feet tall and has blonde hair, was last seen wearing a pink tracksuit, pink shoes and a pink bow.

TBI initially said the toddler hadn't been seen since Dec. 26, but officials on Friday reported that it was more likely she was last seen by a babysitter on Dec. 10 or 11.

Evelyn's mother has full custody of the child. Her father, Ethan Perry, is in the military, stationed in Louisiana. Both the child's mother and father, who are not married, have been involved in the investigation, Cassidy said.

Authorities have asked anyone with information about Evelyn Boswell to contact the Sullivan County Sheriff’s Office at 423-279-7330 or TBI at 1-800-TBI-FIND.

Reach Natalie Allison at nallison@tennessean.com. Follow her on Twitter at @natalie_allison.