Since they are your friends, you can trust them by asking them how to deliver the news to others. By doing that they will not only be aware of your intention of leaving, but also they will provide you feedback about how to inform your departure. Since they know you and your other friends, their feedback is by far the best you can find.
I did something similar when I was trying to gather some friends, it was always a nightmare the process of invite them to lunch or drink. I was so frustrated that I talked to some of them individually about the problem, they listened to me and gave opinions, trying to improve our chances to have regular meetings. I feel that by talking to each of them, they felt part of the solution.
By making them part of the solution, they will understand better your motives.
Choose one of them, explain him/her your motives, your decision and your feelings. You already know the question:
How to tell friends I am looking to move away?
Then just listen, after that jump to the next friend and repeat. After two o three conversations you'll be confident enough to talk to the rest of them. You need to be fast talking to them, to prevent early conversations between them.
In case you don't trust on them enough, change the question to:
How to tell my family I am looking to move away?
How to tell in my job that I am looking to move away?
Decades ago, when I decided that I wanted to travel a lot, visit the world, go around the globe, meet people, discover new countries, I was always talking about that with friends or acquaintances. Not that the main purpose was to inform them, like you want to do, just because I loved talking about my dreams. And it was no surprise for them when I "jumped ship" and joined a crew to navigate the oceans. I think that what I did back then can work in your case too.
I was always saying:
[ watching picture / TV show / magazine ] wow! wish I could go there! you see that mountain? That sea? That lanscape? sooo beautiful...
I want to travel to [ A / B / C ] because of [ X / Y / Z ]
I've always dreamed of these countries / people and about going over there...
as soon as I have an opportunity, I'll go [ here / there / somewhere ]
If someone offers me a job there, I'll pack and go right away!
And so on... Many many times did I do that, so it was no real surprise for them the day I told them I had a chance to move and travel. I had to answer questions about the why's and how's, sometimes, but these were friendly talks, and mostly interested in discussing the countries, places, cultures...
I would recommend doing that. Show interest in moving and traveling. Have small talks with your friends. Talk about opportunities, let them show interest too. And let time do its job...