Assume that the Department of Homeland Security will read your posts
What you put on a social media site is not only seen by your "friends," Over the last 5 or more years, we have seen USCIS google applicants for immigrant visas to determine where they have lived, with whom, and how they live their lives. The US Immigration & Customs Enforcement (ICE) has called in persons to ask them about changes in their relationship status on Facebook, and USCBP has searched the cellphones and laptop computers of persons arriving at US ports of entries. Facebook, MySpace, LinkedIn and other common internet sites are routinely checked by the government. In most cases, these government searches do not violate the law.
Be aware of the immigration benefits you are seeking and make sure your online profiles are not inconsistent with your request
If someone's Facebook page says they are single and they are applying for a green card based on a marriage, expect USCIS to question whether the marriage is bona fide. Likewise, if you are applying as the unmarried son or daughter of a US citizen or lawful permanent resident, expect problems if the social media site indicates you are married. If applying based on a particular offer of employment, be aware whether your online profiles contradict the offer, for example many persons may put an online resume on LinkedIn or other social media site. Any contradictions may raise questions about the legitimacy of the offer.