Please help me with In-game Background?

Hi,

I want it so when someone joins the game there is a moving particle background, I have the particles set up (looks like this: http://prntscr.com/77nr5f) and of course it's moving so when a player joins the game I want it to look like this: https://vid.me/qhG7)

Can anyone please help me get the background like this?

Thanks