Veterans of past wars have long found companionship over beer and conversation at their local veterans hall. But many of those who fought in Iraq and Afghanistan seek that companionship elsewhere — online. Hoping to tap into that virtual community, a public service campaign starting Tuesday, Veterans Day, encourages Iraq and Afghanistan veterans to log onto a new social networking site called “CommunityofVeterans.org.” The site was developed by the nonprofit organizations Iraq and Afghanistan Veterans of America and the Ad Council.