Young people 'hanging about' in a group are not necessarily involved in anti-social behaviour. They are part of the community and should be able to meet their friends in public spaces just like the rest of us.
However, if they are rowdy, use unacceptable language towards passers-by, cause criminal damage or any other specific problem, action should be taken.
Young people should also be aware that, even though they may be doing nothing wrong, simply by being in a large group they can appear intimidating. By making it easy for people to pass you by, having a little thought for others, even smiling, you could make people less likely to complain about you!