I nees to purchase a font, at least ask for it for its owner.
His name is Sergio Luis Coelho and the font is in this link: https://www.dafont.com/sergio-luis-coelho.d742

How can I get in touch with him?

Well it seems that is going to be difficult for you to do, because he didn't provide any contact information whatsoever. Only way would be,
to search his name, and see if you can find a website/behance of his maybe.

Reaching font designers is always tricky. Typically, those who want to be reached will leave contact information, while those who don't (leave an email or website) typically post fonts they DON'T own the rights to, but whom the original designer is unreachable (i.e. they most likely died with no next of kin).

That said, it's always best to TRY contacting the font designer, but if contact information ISN'T provided, it's best to give up on using it for professional uses. If you insist on using it anyway, then clearly state (when you use it) that you make every possible attempt to reach the designer, and ask they contact you (and be prepared to give it up if someone contacts you someday).

By the way, I deal with this frequently, as I'm an independent-publisher who typically uses a different font with each book/series.