How to find a contact has blocked u?

Well from personal experice. Try and find out his personal detail like work, phone numbers housing location. This takes serious time and planning. Try to get information through their friend network. Once all the needed info has been obtained. Buy yourself a decent camera that can be used in night dark, if u want to be serious get some infra red attachments. Take photos of his daily routine. But ur self a black van. Park outside his house have a camp out for a bit. Plent of food and beverages are needed as you could be in that van for a while. This should get u close enough to his current location. You can figure the rest out. I advise you though, do not try to stalk him of any kind. That can land u in some serious trouble with the feds.