Is it permissible to abbreviate "Alhamdulillah" by writing "hmd" on Facebook?

It is not appropriate to abbreviate "Alhamdulillah" (Praise be to Allah) or the salutations upon the Prophet, peace be upon him, as scholars have explicitly prohibited this. The salutations and peace upon the Messenger must be written in full when he is mentioned, as should the praises of Allah with phrases like "Azza wa Jall" (Mighty and Majestic) and "Tabaraka wa Ta'ala" (Blessed and Exalted), completely and without abbreviation.