Click on your avatar (with the two 'jelly men') above, Bloaterbum. From there you can view all of your old questions and answers. If you spot your old friend on one of those threads, click on their avatar to see if they're currently active. If they've ever asked any of their own questions, you can post on one of their threads (even if it's several years old) to try to contact them. (They should receive an email stating that they've got an answer, directing them to to the relevant thread).
Chris