This is a difficult sociological question to which few laymen have answers substantiated by data. One thing we can teach you: "slang" is an uncountable noun, and so we always say "slang" and never "slangs". Individual words are called "slang words" or "slang terms". Slang is a device to reinforce tribal identity. You may be interested to know that in Britain, slang is not necessarily a "street" or an internet phenomenon. Slang has for a long time been a feature of elite private schools. Teachers are known as beaks in one school, for example. That is school slang. At some schools, new pupils are required to take a test on school slang. Sociologically, that is an initiation rite.

In America most of us only use slang often with close friends. We very rarely use slang at work unless everyone is young. Online is the least formal way we communicate, so you will see a lot more slang among American when they are using texts, skype, or facebook.