"I can't really give any more detail other than to say we're still in the preliminary investigative stance and we are working with state authorities," said Debra Weierman, spokeswoman for the FBI's Washington field office.
Florida authorities announced their own criminal investigation in November but have remained tightlipped on the status since then.
Foley resigned Sept. 29 after being confronted with the lurid messages to male teenage pages who had worked on Capitol Hill.
He checked himself into an Arizona facility on Oct. 1 for what his attorneys said was treatment of "alcoholism and other behavioral problems." At the time, his attorney said Foley was gay, an alcoholic and had been molested by a priest as a teenage altar boy in Florida.
Attorney David Roth maintains Foley never had inappropriate sexual contact with the minors. He has declined further comment on any aspect of the case.
Federal law generally requires a person to meet or attempt to meet a minor for sex for it to be a crime. However, under laws in some states where the Florida Republican communicated with minors, an attempt to seduce the victim might be enough for a criminal case.
Under state law in Florida, where the age of consent is 18, a crime may have been committed if Foley is simply found to have seduced or attempted to seduce a minor using lewd or explicit language.
"It's definitely still an active investigation," Florida Department of Law Enforcement spokeswoman Kristen Perezluha said Wednesday.
Foley emerged publicly in West Palm Beach on Nov. 17 to attend a wake for his father, Edward, who died of cancer, but has rarely been seen in public since.