I haven't seen any advantage of wechat over QQ - but both are tencent software anyway.

China is two-faced about things like google (gmail google earth googledocs)  or dropbox or facebook (and so-on) ... on the one hand they ban them, but advertise and promote their own approved version.  They simply don't care how difficult this makes it for travellers in China.

in Indonesia also! But not more popular like Whatsapp, LINE, or BBM

Wechat is the popular in China.

I registered Wechat because I would like to have Chinese friends, because facebook and Line were blocked in China.

Recenly, I watched advertisement on TV.

It was a campaign to persuade people to use Wechat.

Now some Thai people use Wechat.

As far as I am concerned, 90-95 % of Wechat users are Chinese and 5-10% are people who are learning Chinese. 

Most people are using skype, facebook, line, twitter etc

I think Wechat is not popular outside China because it requires a lot of permissions on mobile phones that other apps don't and because it is difficult to modify your profile without googling the insyructions. Since google is not accessible...

Also, wechat is not practical because it is difficult to keep history,  you can't use the app and the web version interchangeably, like you would with FB for example and it is difficult to save and download attachments.

In China, Line wasn't blocked. I use Line, Skype, QQ, Wechat. Some Europen friends of mine also use Wechat, but no so popular.