Gus won a trial with Germinal Beerschot (Belgium) earlier this year. http://foot.tv/news.shtml?newsId=1191 However, he doesn't appear to be there any more. Not finding much using his American, or Greek (Kostas Karterouliotis) names. There was the trial last year -- somewhere in Spain, I think -- but that didn't seem to pan out either.
That's the guy. Still young. Actually, I think last year would have been his last at Olympiakos if he (and his dad, a former pro player himself I think) hadn't bought out his contract.
He certainly looked out of his depth in MLS. A second-tier league or lower division -- or perhaps a larger club's reserve team -- is probably where he'll end up. As I assume he qualifies for EU status, he might as well stay over there and try to make some money!