If you have less than five lives, you can click the heart icon in the top left hand corner of your screen and then select the "Ask Friends" button. Clicking this will bring up a screen where you can search by all your Facebook friends. If you want to look for specific friends, you can use the search bar to find them by their Facebook name. Please note, you can only send a person a life once every 24 hours.
Sugar Smash: Book of Life Game GUIDE