Giphy is a search engine dedicated to animated GIFs. In a few clicks you will be able to find the best animated pictures on the web! For this purpose, Giphy provide several tools:
Search by keywords
Search by categories
The "Reaction GIFS" tab: To respond to comments or posts from your friends on Facebook, you can make use of an animated GIF! The "Reaction GIFS" tab offers GIFS for different types of reactions: a smile, a discontent, an exclamation, joy etc..