MINNEAPOLIS — A new online database promises to crack some of the nation’s 100,000 missing persons cases and provide answers to desperate families, but only a fraction of law enforcement agencies are using it.

The clearinghouse, dubbed NamUs (Name Us), offers a quick way to check whether a missing loved one might be among the 40,000 sets of unidentified remains that languish at any given time with medical examiners across the country. NamUs is free, yet many law enforcement agencies still aren’t aware of it, and others aren’t convinced they should use their limited staff resources to participate.

Janice Smolinski hopes that changes — and soon. Her son, Billy, was 31 when he vanished five years ago. The Cheshire, Conn., woman fears he was murdered, his body hidden away.

She’s now championing a bill in Congress, named “Billy’s Law” after her son, that would set aside more funding and make other changes to encourage wider use of NamUs. Only about 1,100 of the nearly 17,000 law enforcement agencies nationwide are registered to use the system, even though it already has been hailed for solving 16 cases since it became fully operational last year.

“As these cases become more well known, as people learn about the successes of NamUs, more and more agencies are going to want to be part of it,” said Kristina Rose, acting director of the National Institute of Justice at the Justice Department.

Before NamUs, families and investigators had to go through the slow process of checking with medical examiner’s offices one by one. As the Smolinski family searched for clues to Billy’s fate, they met a maze of federal, state and nonprofit missing person databases that weren’t completely public and didn’t share information well with each other….