Some of the suppositions on this thread are incredibly inappropriate and should be edited or deleted. Why? because this person you're seeking is probably LIVING. This is a public message board on the internet, the data will return in a google search. If I were this "maybe" 1/2 sibling, and found my name and anecdotes being mused over, you would be the last person I would want contact with.

Post a simple "looking for" on the Lost Friends and Family board. A name, a general location and a time frame can be posted without violating the privacy of a living individual. Save the thinking out loud for a private discussion.