A good start to find new platforms is to have a look at one of these pages:
Once you have targeted a decent platform you have to find good footprints for the search engines. What I do first is to google for "powered by XYZ" (XYZ= platform name) because many engines use this footprint. If you don't find anything related to the platform try another search like "XYZ" demo. Often times you find a demo page to search for suitable and unique footprints. This is often the case for platforms which are supported by softaculous.
A good footprint is unique to the platform and can be found anywhere on the page ("Howdy, Stranger! It looks like you're new here.") or in the url (inurl:"wiki/members.php").
Once you have found a suitable footprint you create a basic script for GSA in an editor.
page must have=Footprint (without quotes; no "inurl:" footprint!! take a look into existing engine files to get an idea of it)
description=Platform (Wiki, Forum, Blog, etc.)
search term="Footprint 1"|"Footprint 2" (with quotes " " if it is a multi part keyword)
Save your edited script, rename it to "My Engines - XYZ.ini
" and paste it into your engine folder (...\Program Files (x86)\GSA Search Engine Ranker\Engines)
. If you have done that (re-)start SER and crawl some URLs with the "Search online for URLs"-Tool (Options -> Advanced -> Tools)
, save your results to a custom file and let SER find some URLs for you