I was reminded of a disappearance of a teenager visiting the UK that I followed recently.
Thread here, it is not that long for the lack of new developments:
UK - UK - Yafiet Tesfalem, 17, was on school trip from Denmark, YHA hostel, Manchester, 21 Mar 2019
This Eritrean refugee living in Denmakr was on a school camp with his class and accompanied by teachers. He had a secret phone and one morning he called in sick. Instead of going to bed, he disappeared from the campus. LE concluded that his disappearance was planned.
IMHO it is 'old thinking' that teenagers will be safe when they are on a tour with a supervising adult, as appears to be the case of Linh Le too.
There is a whole world lurking in their phones and they may be up to no good, even when the supervisor sees them all quietly sipping tea.
The Danish group returned to Denmark too, I am not surprised that the Vietnamese travel guide did the same.
Is anything known about the background of Linh Le?
My first impression was that she might come from a well to do family for them to be able to afford this trip.
Another possiblity (apart from grooming & meeting the wrong guy on the internet) is that this trip would have been cheaper and more comfortable than hiring a smuggler.
I hope she is unharmed and found soon.