Rainwalker went missing Nov. 1, 2007 when he was 12 years old.
Police hope the reclassification may prompt someone who knows something about Rainwalker's disappearance to come forward with new information.
In a press conference Thursday, police said they have no specific new evidence in the case despite running down as many as 500 leads.
Senior state police investigator Thomas Aiken said "this is not a cold case, it's a continuing case. We've never stopped, we will never stop."
Rainwalker's grandparents were also on hand for the press conference. His adoptive parents, Stephen Kerr and Jocelyn McDonald, were not.
George Bell, chief of the Cambridge-Greenwich Police Department, said that he has not had direct contact with Kerr but has been in contact with his attorney. Bell said it is possible he will interview Kerr in the future.
Representatives of the FBI, state police, state park rangers and the Cambridge-Greenwich Police Department were on hand for the press conference.