Telegram is indeed one of the easiest way to scam people who want to make thousands of dollars overnight. When you respond to their first message and seem interested then they know you are one of the gullible greedy ones so they continue to scam you. You friend need to join this forum to learn how to avoid such scams.

Your friend also need to know in the street of crypto and internet, you can't trust anybody. I hope that wasn't his last penny and i hope he has learnt his lessons.

When it sound too good to be true 'Guaranteed double or triple gains' (It's a scam)
When you need to pay to be able to withdraw (It's a scam)
When they start the conversation with 'hello friend or hello sir' (It's a scam)
If they try so hard to show you documents and license to be able to take money from you (It's a scam)