Thanks for asking this. The way to contact people on the site is to use the profile look up tools. Not everyone discloses their emails or phones or web pages, but some do.
Within the site, the best way to “thank” someone is to share links to their answers, edit (if you’re sure you are making a post better - commenting first if you need an OK to make a big edit), and awarding them bounties.
Also - if someone is here in an anonymous / not easily traceable, consider that they may have reasons to manage their identity - so be sure you are not doxxing someone unintentionally by researching / disclosing information that’s not publicly available or shared by a person / account.
In your case, the profile is set up to share minimum data, so you might need to be patient for them to see and possibly decline politely your generous offer to make contact with them.
I, too, appreciate their contributions here greatly. We should be lucky to have more people like them here. The same goes with people like you that take the time to recognize others for being useful and helpful.