Can't help you on the YC front, but have you tried doing an unclaimed-property search in California (their HQ) or whichever state you were in when you made this

Can't help you on the YC front, but have you tried doing an unclaimed-property search in California (their HQ) or whichever state you were in when you made this investment? https://www.usa.gov/unclaimed-money https://www.usa.gov/unclaimed-money