When the time comes where they desire to boost these demonstrations teams of "Trained" individuals (usually young activists) go in...they align with the local leadership of these demonstrations with money in hand to support them and dangle any carrots needed....from gov. sponsorship to actual leadership visitation.
Things move pretty quickly after that.....generally the local people are by then ready to be led.
If you note in the Gaza demonstrations recently, one of the IDF soldiers said that the Arab elders were trying to calm the youth down, but was noted that EU activists wanted them to riot all the more. Often times these will be people with megaphones...or yelling the loudest.
Same with Ukraines Maidan......the crowds would have not become violent as we saw, without those who assumed control to push through to the government buildings and face down the police trying to maintain calm. Even Maidan demonstrators reported they were being taken over.
Crowds are easily led...that's why they send teams to various countries. And you always see then the nation leaders begin to “visit” and visually support the demonstrations....all carefully timed when they know the tipping point has come.
I followed one team who went into Syria to work the crowds...their next stop was Turkey as things began to grow there....