đó and đấy in many cases are synonyms but people tend to use đó more 'cause đấy is somehow considered as a dialect and it doesn't sound so nice in official contexts. When talking about place (ở đó), or things (cái đó, thứ đó), đó is utterly prefeable. Another variant of đấy is ấy.
Dear Lucy, I miss you so much. What is your facebook? I searched your name (lucy phan) on facebook but I did not find you. It is so many people who's name is "lucy phan". I'm so sad. Please, contact me. You can find me on facebook. My facebook is "Phạm Chí Minh". Thank you very much.