I am not familiar with the website you're asking. But if they're already gone, who are the people that you will chase? do you know them and you have valid proof that they've stolen money to you?
In this case, you should be consulting a lawyer that's expert on this kind of cases if you want to pursue a case but as I've said, you have to provide to those things.
Can they just dissapear into the thin air with our coins?
Sadly, yes and they've just did it.
Well as a start the persons involved with Stakeunited were on this forum and active, it was my lucky guess somebody knows who they are, over i can get information from which country so i can research on:
https://bitcointalk.org/index.php?topic=2622314.320And i will try everything to get my coins back, wouldn't you?
They made announcement about closure here but not to me, who has trusted them with my coins? So i guess they were not all bad intensions, just some mistake....
Yeah, they were here before but the account last login was on 2019. It's been two years since that OP have been gone. I know how it feels when you're money was lost.
But even if you message the account on that thread, it's very unlikely that they will reply to you.