All I know is when they say she may be a runaway, nothing seems to get done, they don't go looking for runaways like a suspected abduction. No crime.
LE have to report any missing child under 18 to the NCIC immediately, by law, but that's just entering them in a database.
800,000 a year, 2200 a day are reported missing (2005 statistic), most return in 24-48 hours.
Since most missing kids are runaways I guess LE doesn't want to run around all day everyday looking for them all, unfortunately, deciding which ones may be abductions is just guesswork.
Parents of Runaways Fend for Themselves
Police Put Off Searching in Most Cases
http://www.washingtonpost.com/wp-dyn/articles/A16540-2005Jan17.html