As justguessingbut suggested, you can find a domain name from project he worked on, and thus his real name, and from there a search will lead you to angel list

As justguessingbut suggested, you can find a domain name from project he worked on, and thus his real name, and from there a search will lead you to angel list which links everything together with dates that match with the op's story. I was able to do it all in less than 5 minutes without anything but a browser and I'm slow... so I would call that really easy.