There are, to my knowledge, three micro layout groups on Facebook, but two of them seem to take comparatively huge layouts, however charming you might consider them.
But all is not lost for those who like 'true' micros. Our own Ian Holmes of this parish has a group with these criteria:
The ONLY Facebook page devoted to the discussion, design and construction of TRUE Micro model railroad layouts. That is “Micro layouts are small model railroads, usually less than three or four square feet in area, that nonetheless have a clear purpose and excellent operating capability".
You can find it here: