There are commercial databases which compile information from utilities, DMVs, magazine subscriptions, tax rolls, etc. The FBI has access to these.
There are databases which get their information from newspaper and magazine articles. Maybe she won a track meet or a cheerleading competition, and her local paper wrote her up.
Driver license files can be run with just a name and an age range. Vehicle registrations can be, too.
He could check phone listings, e-mail address databases, and MySpace and Facebook accounts (and what 16 year old girl isn't on MySpace?).
If he can't find her, he could always find family members, like parents or uncles/aunts. Older people have longer paper trails.
For a higher-priority case, he could always send agents from the local field office out to trawl area high schools with her name and photo (if available).
If she has broken bones or braces, medical insurance claims might exist in her name. He'd need subpeonas for those.
A criminal history check might yield something valuable, though a 16 year old girl is unlikely to have a rap sheet that isn't sealed. She'd be more likely to appear as a victim or a complainant on an incident report.
I assume you're talking about a murder victim?
