In addition to Google, I often use sites such as this one http://www.legacy.com/TheStar/Obituaries.asp?Page=OBITFINDERRESULTS which searches the Obit announcments of the larger newspapers within the US & Canada. Many smaller papers are not listed.
You can narrow the locations checked by State or Province and if you insert "Kingdom Hall" or "Jehovah" in the Keyword field, all obit text will be searched for those words. Include the quote marks in the keyword search to search for multiple words together.
Often announcements will state that a Memorial Service is to be held at the 'Kingdom Hall' without mentioning 'of Jehovah's Witnesses' or if the service is held elsewhere, it may state that the person was 'a loyal servant of Jehovah' or something similar, so you may need to search both keywords seperately.
Unfortunately, the site only displays obit announcments for up to one year otherwise, there is usually a fee for fully viewing older archived announcements.