What kind of services? IM app? Thailand uses LINE, Vietnam: Zalo, Cambodia and Myanmar Telegram and Viber, in Indonesia many uses few IM at the same time.
It is not the IM apps, SE region which I suspect the author is referencing predominately uses Whatsapp.
The value in SE is mostly B2C, instead of marketplace feature, most local tiny(or even big ones willing to evade tax by not having any physical presence) businesses will open a small business or general page and publish their wares as posts. Lives will be used to demo products or services now and then. People follow these pages and flock over to buy things.
In a sense, Facebook and Whatsapp are like Amazon/Aliexpress of SE Asia.
I was there for 5 months visiting a friend(and recovering from burnout), and number of people using such pages to sell anything from basic clothing to food to services are HUGE! It is literally a huge business hub for people to discover and make online purchases. In summary, Facebook pages are the e-commerce front(due to lack of shopify/amazon and similar operators who can handle logistics and payments) for individual businesses.
There were many journalist reports about this phenomenon several years back, but I am too sleepy and tired to link those.
