A former Federal Bureau of Investigations agent has publicly cast doubt on the parents of missing teenager Sebastian Rogers, as efforts to find the boy enter their fourth week.

"No shoes. Dog scent ended at [the] construction site. Step-dad wishy-washy on where he was, publicly," tweeted retired agent Jennifer Coffindaffer, early on Monday morning.

"Not all parents act alike when their child goes missing, but there is a general range. These parents are outside that range."

Fifteen-year-old Sebastian went missing from his home in Hendersonville, Tennessee on February 26. The teen is autistic and missing person posters advise that this "may impair his ability to return safely without assistance."

The Tennessee Bureau of Investigations has worked with Sumner County Sheriff's Office and the FBI to search an area of more than 2,000 miles in an effort to locate Sebastian. Law enforcement have also conducted aerial searches and reviewed surveillance footage.

"Much of the work currently being done to bring Sebastian home may not necessarily be public or visible. But agents, detectives, and intelligence analysts continue to work around the clock to review every bit of information available," the TBI said in a statement on Friday.

"Sebastian's family has remained cooperative since the search began, and have done whatever law enforcement has asked of them."

In their most recent statement, the TBI also emphasized that there was both no proof of criminal involvement but also no proof of no criminal involvement.

"Agents and investigators are reviewing any possibility at all that may indicate where Sebastian is."

In a heartening update since retired agent Coffindaffer's post, she tweeted later in the morning, "This is good news. I learned my lesson years ago about jumping to conclusions when it comes to casting aspersions against the parents of Austic children too early. "

"I will keep synopsising facts and posting information. More hope after seeing this!". The post was accompanied by screenshots where Sebastian's mother, Katie Proudfoot, asked an online commenter who said they spoke to him about his whereabouts.

The commenter, whose name was blurred out, said they did see Sebastian as did a 'guy across the street'.