I have this problem a lot when coming through event logs and I need to find the SID of an active directory user.

If you would like to list all of the SID’s for the users, open command prompt and run:

wmic useraccount get name,sid 
Otherwise in order to find it for a particular user, run:
wmic useraccount where name="USER" get sid
(In my case, I would replace "USER" with "jtyson")