I just want to reinforce what my fellow native speakers have said:
English speakers DO NOT use these abbreviations in our everyday writing. Most of us never use them at all. Some people use them in texts if they are very short of time or have a limit on characters, but in other situations they should never be used.
It goes without saying that they are totally inappropriate in business and academic contexts. What's more, they are also inappropriate in other everyday situations, however informal.
Some non-natives write 'u' and 'coz' and suchlike in their italki posts, and all this does is make bad English worse. When we see a post which begins 'r u', we all know that it has been written by a non-native user, and often one who has a fairly limited command of English.
Andrey, please....do yourself - and everyone else - a favour and forget about all of these useless abbreviations. Just write normal English words, the same as native speakers do.