An easy way to make new friends and find people in similar situations is to go to a few expat meet up events. These groups also bring the comforts of home in organising those little things like Thanksgiving dinners or Fourth of July celebrations.
The London Expat American Meet Up Group - These guys have been organising expat meet ups since 2002. They take into account all interests from sports, politics, drinking and art to a 9/11 meet up and all the essential American holidays. Sometimes a few people attend, sometimes a few hundred.
American Expats in London (Facebook) – 1,800+ members here to share stories, arrange meet-ups and start interesting discussions like where to find NHL games in London pubs, SuperBowl parties and the best Mexican food in the city.