Linda, have you had a look at the list of tags? (that baggage tag icon). We create them as we go along, so that list can get quirky. I don't know if you can first assemble all the posts for any one tag, and then do a word/name search of just those. Lemme try and I'll get back to you in a few seconds.
Just tried: it works very well. Look at the top of your page, select tags, decide which one you want to look through, double click it, all those posts will appear, then click advanced search, if you are not seeing a place to write the name of the posting person. ( "Post by ....", something like this.)
There are several "ITVS + Something else" tags, too.