The US Office of Government Ethics has published their guidelines for using social media. The direction is not for a government account, but "as a general matter, this requirement limits the extent to which employees may access and use their personal social media accounts while on duty." One large section is whether or not a job title can be included in a posting. Another is on how recommendations should be considered. In any case, now that there are guidelines, it's to be noted that this is not the final word:
"In light of the ever evolving nature of social media, the foregoing advice is not intended to be comprehensive. OGE expects to issue additional guidance in the future addressing questions outside the scope of this Legal Advisory. Designated Agency Ethics Officials with questions regarding the application of the Standards of Conduct to social media may contact their assigned OGE Desk Officers."