PALATKA, Fla. -- A 15-year-old girl missing from San Mateo, in southern Putnam County, may be with a 22-year-old man who authorities have named a person of interest in the slaying of a Melrose man.

Late Thursday, the Florida Department of Law Enforcement issued a nationwide Amber Alert for Morgan Amanda Leppert, saying the girl is considered to be in danger.

Leppert has blonde hair and blue eyes, is 5 feet 1 inch tall and weighs 114 pounds. She was last seen on April 22.

Authorities believe the girl may be with a man she had been dating -- Toby Lowry, 22. A warrant has been issued for Lowry on charges of larceny and interference with child custody, with no bond and nationwide pickup.

Lowry is described as having blond hair and green eyes. He stands 6 feet 2 inches tall and weighs 190 pounds.

Investigators believe the two are traveling in an aluminum-silver 2003 Toyota Tacoma four-door pickup truck with Florida tag number 193KLR.

According to the Putnam County Sheriff's Office, the truck is registered to 64-year-old James Thomas Stewart, who was found dead in his Cherry Laurel Drive home at 10:24 a.m. Thursday.

Putnam County deputies checking on the welfare of Stewart, who had not been seen for several days, found the man's body.

Investigators said, "foul play was apparent," but they did not provide details of how Stewart was killed.

Puntam County authorities said Leppert and Lowry have been sighted in the victim's vehicle within the past two days and that the two may have traveled to the Houston area of Texas, according to PCSO.

"We have information that they might be in a certain vehicle, and we got a few hits from officers or from other states running this tag number and we think it may be in Texas. Again, we're not certain of that at this point," PCSO Capt. Rick Lashley. "She could be anywhere in the United States right now."

Lowry has been named a person of interest in the homicide investigation of Stewart's death.

Anyone with information about either Leppert or Lowry is asked to call the Putnam County Sheriff's Office at 386-329-0800 or the FDLE Missing Children Information Clearinghouse at 888-FL-MISSING.