I've seen some people that were advertising their business through myspace and hi5. Is it worth it? Or are they already dead social medias?

Myspace is dead right now. Justin Timberlake has been trying to bring it back as a music community, but I'm not sure how well it'll take off...we'll see. I've never even heard of Hi5. Pinterest, Facebook, Twitter, LinkedIn, Instagram...that's where your focus should be. If you have extra time, you can always try the other sites that you're talking about, but I would put more of an effort into the popular sites.
Nobody has used Myspace since 2009. Myspace i definitely not worth your time. Besides . If Facebook, Twitter, and YouTube haven't worked for you. You might as well give up. Everybody uses those sites, so they should be sufficient. You are never going to find a better audience then those.
It's just business.
I wouldn't suggest those two sites at all. The last time I went on MySpace was about 6 or 7 years ago. I haven't even heard of Hi-5 and apparently other people in this forum haven't as well. This clearly states that people don't really go on these sites, so you'd practically be advertising to no one. It's a waste of time, effort, and again, TIME.
Promote your business on useful social networking sites, the ones people actually use today and get rid of accounts on outdated sites such as Hi-5 and MySpace.