People are allowed to voice their opinions on social media as they are allowed to voice them in person, simply because you don't agree with their opinion (particularly where it is about you personally) does not mean this is a crime or that the police can take action.
However, there is a difference between someone being rude, argumentative or having a different point of view to yours and you receiving threats or targeted abuse.
Depending on the circumstances and the nature of the messages, you may wish to deal with this yourself by 'unfriending', 'blocking' or 'unfollowing' that person so that you do not have any further contact with them. You can also make a report to the relevant social network who all have help and advice pages about how to deal with unwanted contact or report unsocial messages, they may under the right circumstances be able to simply remove the content and/or close down the person's account.
These sites can also help you manage your security and other settings as well as give parents advice about how to keep young people safe online.
If a person sends threatening/abusive/grossly offensive messages to another person via Facebook, Twitter, or any other social networking site, they could be committing an offence. The most relevant offences are 'harassment' and 'malicious communications'.
For harassment to be committed, there must be a 'course of conduct' (i.e. two or more related occurrences). The messages do not necessarily have to be violent in nature, but would need to have caused some alarm or distress.
If there has only been a single communication, which would be insufficient for the offence of harassment (above), there could be an offence relating to malicious communications. For such an offence to be committed, a message must be sent to another person (or sent via a public communications network) that is indecent, grossly offensive, obscene or threatening/menacing.
If you have received any threatening/abusive/offensive messages via a social networking site, and believe that an offence may have been committed, you can report this to us here online or via the telephone on 101.
To help the police in investigating your case you take take some simple steps to record what you have been sent: