If someone gives you information via the internet, how credible, if at all is it in a criminal investigation?

I believe it's ''credible'' if you call it that up to a point. But not substantial evidence.

Would it be enough to be cause for an investigation?

Depends on the seriousness of the crime, and what you were told/saw. If its something serious you saw on a site, get the ip with dos ... go to dos... ping www.whatever.com
and visual trace the ip, then contact the isp. If it's something else post a little about what happened.

Info posted on the internet isn't credible in the least as regards to a lawsuit. You need to back it up with credible, published proof. Perhaps that proof would be referenced via the net site. You would still need the verifiable information.

whether it is credible is up to the jury and the judge. but in this country it is sadly true that it can be considered probable cause for an ivestigation.

Thanks guys! That's what I needed to know!