If you are an Immediate family member of this person then you can go here:
Navy Together We Served
And create a profile for a Fallen, Deceased or MIA Navy Sailor. And it may be a long shot but maybe someone on there knows this person or served with them. I have reconnected with quite a few old shipmates through TWS, granted i only got out 4 years ago.
The more info that you know about them, like when and where they served at or what commands they were stationed at the easier it will be to find out more info on them. I did see a section on there where you can start a forum thread requesting information about deseased or missing service members.
Also any active duty, retired, or navy vets, this is a great site and I highly suggest creating a profile. it's free for the basic membership.
And there is one for all you other military folks (Army, Air Force, Marines) out there too:
Together We Served
Except for the Puddle Pirates
, haven't seen a Coast Guard one yet.
Good luck man I hope that you can get some info on them.