Wholesaling-How are properties found?

[Kenneth Goldman]

I have listened to many real estate investors talk about marketing methods used to find properties such as yellow letters, postcards, direct mail...etc. One in particular even describes the amount of mailings his people send out on a monthly basis. But I want to know is how the properties are first located to target a certain area with my yellow letters. Is there a list to buy or do I just circle a neighborhood on the map and target every address? However that does not make sense either as not every house on the block needs rehabbing, is in distress or is the type of house that I am looking for. I beg for direction.