How to limit the presence of non-property owners

I am the President of the Owners Community of a block of flats and the other day a neighbour complained that there are some teenagers who hang around in our flat entrance with a friend who is a property owner. They sit on the steps chatting and smoking. The neighbour complained the teenagers shouted at her - she didn't understand them because she hasn't been living here long and doesn't know much Spanish. What should I do as president. Do I have the right to send them away even though they are accompanied by a neighbour? And what can I do if they ignore me?

Lawyer's answer:

The best action to take is to ask your community administrator to call a Community meeting with just one motion: to pass a new rule governing the use of the entrance space. With the approval of the Community you would have the authority to ask them to leave. In these cases it is often useful to put up a Private Property sign beforehand, forbidding the kind of gatherings you describe. Then you will have even more authority to ask noisy troublemakers to leave and to call the police if they refuse to do so.