Hi there,
I haven't specifically tested with 1.6.x but I would suspect that the JomSocial developers haven't changed their table layouts significantly so as to break the search plugin.
I am working on a demo site and will be able to confirm 1.6.x compatibility within a few weeks.. also adding a few new features like:
fetching group/user thumbnails
controlling which areas are allowed to be searched, and
displaying users by username or full name, and
maybe even searching custom user fields
I'm swamped with billable work at the moment so these upgrades are taking a bit of a lower priority, unfortunately (?)
Cheers,
Chris .\\