訪ねる is informal, can be considered as just one of a set of actions, and contains an implied purpose for visiting:
Mr Obama visited Hiroshima and laid flowers at the Memorial (implying perhaps he visited to pay his respects???).
With the informal 訪ねる, it's likely "visiting your friend's house" is contracted to "visiting your friend" in everday usage as your listener expects from the verb that your friend will be at home。 If you were catching up with your friend elsewhere, you would more likely state the location, use a verb such as 会う, and say something to the effect that "you are going to 'meet' your friend at a cafe".
訪れる is more polite and 訪問する more formal and are used when there is an explicit purpose for visiting a place:
The President of the United States, Mr Obama, visited Hiroshima...
(explicitly) emphasizing his pursuit of the ideal of a 'nuclear-free world'.
[Examples are from the 2017 News Kentei Guide]