Yelp is not a search engine, they have however made a deal with Bing which I believe is Microsoft's search engine.
Ya yahoo uses yelp to!
You create your own yelp page for business!
Apple or Siri by default uses yelp!
When you say hay Siri where a good place to eat!
Ask someone with and IPhone to show you.
But ya it’s a business listing site per se not a search engine for looking up everything!