How do I catch a SMS spammer who is using google voice to spam me?
I have the google voice number and 2 of their burner emails with gmail. How do I gather enough information to inform the authorities?
Don't play cops and robbers, just report the issue to Google and they will take care of it. Google and the authorities have better tools and people who are paid to deal with these criminals.
That being said, one way to identify someone online via chat or sms is to get them to visit a URL. This could load a page that logs the IP address, and then you can perform a whois or geoip lookup on this address. More advanced/blackhat/illegal method would have that URL return a page that exploits a vulnerability in the browser and then you can collect personal information from the spammer's machine.