If you are looking for PPT search engines here are two options to consider. Keep in mind that there are no real quality search engines that are entirely dedicated to PowerPoint presentations. I mean quality search engines  because you will find some out there but not worth mentioning here.  I tried many platforms and I landed the two options below. 

1. How to use Google to search for PowerPoint presentation? 

The first option and the one that I prefer is using Google Search  engine. Several people disregard this handy feature in Google that allows you to narrow down you search to specific file type. You can easily search for documents by file type using Google Adavcned search.  Files supported include PT, doc, PDF, rft, swf, kmz, and many more.
Here is how to search for PPT presentations in Google: First type in your search query, click on  Advanced Search, and scroll down to file format and choose PPT or any other file format for that matter. Watch this video to see this hack in action

2. Slideshare 

Slideshare is not a search engine but rather a content sharing platform where you can search for, access, and share presentations and infographics. You can use the site’s search engine to look for PPT presentations or you can browse through the collection by topic. Presentations are arranged into various categories including: Education, Art & Photos, Business, Design, Engineering, Environment, Internet, Food, Health & Medicine, News and Politics, Self improvement, Science, Technology, Sports, and many more.