Sullivan County Sheriff Jeff Cassidy told reporters Wednesday that his office is working with state and federal authorities to find Evelyn Mae Boswell.
"We remain committed and continue to do everything possible to find out what happened to Evelyn," Cassidy said. "Our main concern right now is finding Evelyn."
An Amber Alert was issued for the girl after she was reported missing Feb. 18. That was least seven weeks after what's believed to be the last time she was seen.
The Amber Alert was issued after police received a referral from the Tennessee Department of Children's Services saying family members hadn't seen the baby in about two months, the Bristol Herald Courier reported.
The girl’s 18-year-old mother, Megan Boswell, and grandmother are now in the same Tennessee jail after giving conflicting accounts about her disappearance.
Frustrated by the women's multiple versions of what happened to Evelyn, authorities said they charged Megan Boswell with filing a false report because her conflicting statements have impeded the investigation.
Megan Boswell is in the Sullivan County Jail. Her mother, Angela Boswell, is being held there as well, on charges of theft and violating probation in an earlier case.
Court documents from Megan Boswell's arraignment Wednesday accuse her of initially telling state investigators that Evelyn Mae was with the child's father, Ethan Perry. But he's serving with the U.S. Army at Fort Polk, La., and did not have the girl, WJHL-TV reported.
Megan Boswell later said her mother took her daughter to a campground in Mendota, Va. Authorities then searched multiple campgrounds in that area and found no sign of the girl, according to the station.
Angela Boswell and her boyfriend, William McCloud, were arrested last week in North Carolina on fugitive warrants unrelated to the toddler's disappearance.
Angela Boswell was returned to the Sullivan County jail on Monday evening and arraigned Tuesday on a theft charge. The judge set her bond at $5,000 in the case, but Sullivan County Sheriff's Capt. Andy Seabolt said she will remain incarcerated because a bondsman revoked her bond in another unrelated case.
Megan Boswell was jailed Tuesday night, and her bond was set at $25,000, the sheriff's office said.
The Associated Press contributed to this report.