I'd think that it will depend very much on what you search for:
do you expect the person to respond, e.g. put up whatever scrap of reflective material they have with them when they see your search-light?
In that case, and open landscape a highly brilliant lamp would be good: you could sweep a large space slowly with such a light and look for reflections.
E.g. I can see the reflective background in the eyes of the neighbour's horses across the valley (ca. 800 m, 1100 lumen light IIRC) without problem. You could similarly detect reflective material.
Do you have to seach in bushes where you anyways cannot see far?
In that case, less brilliant but wide angle is probably better (but I'd guess that chances are pretty small to accomplish much before the next morning). Brilliant and tightly focused light in such a situation will possibly be more of a hindrance than a help: it can easily blind you enough to see nothing at all outside the narrow illuminated space, and even in the direction of the search light nothing but the bushes in the foreground.
I guess the most sensible thing would be to try covering easily accessible and sensible places rather than going right through the bushes during the night: along roads/trails where the lost person is likely to be and where your light can actually help. If you can expect the person to be responsive, then acoustics may be your friend - better if organized: shout / whistle in a concerted fashion, then stop to listen.
Are you looking for someone who is hiding or unable to respond and cannot be expected to have anything reflective on him? You really need to search through the bushes?
Then, maybe night vision gear would be better than search lights. Or search dogs. If you have to do with lamps, you'll need a massive group helping with the search to cover a decent area in one night.
I think that headlamps, torches and rescue lights (e.g. head lights of fire fighter trucks) are optimized towards a very different purpose: they are optimized to brightly illuminate a restricted space. Head lamps e.g. are useful to enable you to work, e.g. repair something or care about an injured person. But even though mounted on your head, I find them illuminating an uncomfortably small angle for e.g. hiking or in a cave. The torch I mentioned above is also good if you want to repair something, but it is useless if you want to search in bush terrain.
I find that head lamps are often a pain for a group: most people are polite enough to look into your face when speaking or being spoken to. Which will blind away your dark adaption over and over again...