a little five year old girl went missing here in town. What house would you use to represent a lost child, possibly a runaway, but more likely abducted.

Whose child is she, in relation to the querent?

no relation...just a concerned citizen.

Here's something from this web site:

"If a question is asked regarding a mundane situation in which the querent is not personally involved but has a strong sympathy and inclination, then use the 1st house to represent the party the querent favours and supports."

http://www.skyscript.co.uk/temples/h1.html

Can't the 5th also be used?

This issue has come up a number of times on this forum with no easy resolution. One idea is that if you can't put yourself in the chart then perhaps you shouldn't be asking the question (this is, of course, apart from those you ask as the astrologer for a client). I am inclined to go that way myself. Horaries need a commitment to the question, not a second hand curiosity. I do not mean to imply that the question or the concern is not genuine, just that I think these sorts of charts can lack the real connection that horary requires.

My solution to this is to use the time of last sighting. If you can track down the time that the girl was last seen you can draw up an event chart from that. Then give the girl the ascendant. This chart should be able to tell you whether she has been abducted or has run away. Let's hope it is the latter. We have done this a number of times on this forum with suspected abductions.