In addition to what was said below, you can private message individual responders to thank them. That can take a lot of time, so only do it if you have more to say than just "thanks," or if you have something to say that's kind of private and not for everyone to see.
If you comment in the SWH section, some people may not see it. They won't get a notification via email so they'll only see it if they go back to check subsequent responses - which some people do often, others don't. Same goes for responders who edit their answers - you won't know it unless you go back and re-read or at least skim to see if they wrote ETA ("Edited To Add") to their original answer.