A security guard approached and separated the group. One of the teens took this opportunity to kick the man in the leg.
It was reported to Invercargill Police.
A police spokeswoman said they will not tolerate anyone, regardless of their age, using violence and intimidation against other members of the public.
"This is assault and anyone who is found to be involved in activities such as this can expect to face criminal charges.
"Police cannot be on every street corner every hour of the day and rely on the public to report any observed suspicious and criminal behaviour.
"If you see something, tell us immediately. We will do something about it."
The spokeswoman said anyone who sees incidents such as this should call 111 in the first instance.
If anyone has any further information regarding this assault they should report it to their local police station.