messages extension in the share menu does not work
I am using sierra as well I did what was suggest here:

I unchecked the contacts on icloud settings and then tried the share via imessage and it worked. Then I checked back on the contacts on icloud contacts and it worked again

I did this from safari, when I tried from a file folder it did not, so I went back to uncheck the contacts on icloud and repeated the sequence described above and it worked

It seems to me that from each place you want to share something via imessage you have to turn off contacts, try it, turn it back on again and this seems to correct whatever it is that was wrong

But after a little while it stops working again if you have contacts activate in icloud

I guess the next step is to try to loggoff from the icloud account and re login to see if this gets fixed