Hej Peter,
I thought I'd chime in here as well, since we're (Refugees United) are a non-profit building an on-line tracing system for Refugees (and others looking for family) at
http://refunite.org/.
Our approach is somewhere in between the complete openness of person finder and the strictly closed systems used by the ICRC and others.
It's worth mentioning that our main target is Refugees, and as such we often deal with a much longer term displacement than the typical disaster relief situation. Also we have a international, cross.conflict database, and as such deal with people who have no issues registering in a public system as well as refugees from armed conflict who may have different issues.
The system has been online since november 2008, and we're currently on our 3rd iteration, and have recently added mobile (sms and browser-based) tools to the palette.
The idea behind Refugees United is that people register themselves with whatever amount of information they feel comfortable with. In many cases that information is similar to what personfinder collects, but we have a lot of fields that allow for anonymous registration, i.e. with nicknames, scars, birthmarks, memories from childhood etc.
This information is openly visible online. People can then search for missing family, and if they find someone they think might be family, there is a closed (secure) message system on the platform that allows them to contact the other person without revealing infroation such as e-mail adresses or phone numbers.
Precisely for reasons of privacy we don't let people register who they are looking for, but only themselves.
And with respect to minors, it's something we're still trying to figure out. We're just entering into dialogue with a group of International Aid orgs that work with displaced minors. At the moment what we do is to discourage minors from registering, and to throw away the age field of anyone under 18. The latter is to avoid traffickers etc. specifically searching for groups of minors.
We're in dialogue with personfinder and others about ways of sharing information between the systems built for immediate information sharing, and our system, which is better suited to longer term refugee situations.
Feel free to ping me with any other questions you have.
Regards
/Tomas