Dear brother Khurram
Assalam u Alaikum Wa Rahmatullah-e Wa Barakatuhu
Your question is very significant as it pertains to a very common situation that is faced by many on daily basis. The basis rule of Islamic Shariah that should always be kept in mind regarding the holy name of Allah the Almighty and other sacred names or words is that they deserve respect in its highest degree and that respect should be observed/paid depending on the language that people are communicating in or norm of the time. So the languages and norms vary greatly. In some languages, respect is shown in one way whilst in others it may be shown in another way.
Now once you have understood the basic principle of Shariah regarding respecting the holy/sacred names, now we can address the issue at hand.
In English language, any proper noun is supposed to start with a capital letter. Now violation of this grammatical rule will not automatically be considered a violation of Shariah but depending on one's intention it can regarding the sacred names. If someone's intention by deliberately writing the sacred name without capitalizing the first letter is to disrespect then it would be understood as such.
Since capitalizing the first letter of any proper name is required by rules of English grammar, Muslims should always capitalize the first letter of the name of Allah or other sacred names. However, writing the entire name in capital letters is neither required nor obligatory.
The above advice should apply to all writings whether they occur on facebook, twitter, whatsapp, email etc...
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America