You could try some creative searching on Google ...
"his first name and surname" in inverted commas
any nicknames which he may use eg Michael/Mike plus surname in inverted commas
If you don't get the results you want add an area or specific city.
To the search you can also add his mother's first name with or without her surname. If he was registered under his mother's surname, he may have kept her surname. If he knows your father's surname he may use that (even if not officially registered with that surname). If his mother went on to marry and changed her surname, your half brother may also use this surname.
So you have a few options to try ....
When you can use the PM system we may be able to look for a possible marriage for her which might give you another surname to search.
