Working with a remote team can be challenging, but it doesn't have to be. Here are some things I've done that helps with dealing with contractors working remote.
1) You're a project manager, assign them measurable projects, it's far less stressful for both of you to have a clear and concise deliverable that they are expected to give you by the end of the day, 2 days or a week (not sure which projects you're dealing with, but it shouldn't matter). Make sure they are not too long (under a week) to make sure they are actually working and not procrastinating. Also ask them how long does each task takes them, or will take them, and expect to quote this back to them if they are asking for extra time (but be reasonable).
2) Trust them, this will give you peace of mind, and it will make them more responsible (just like children, or a new girlfriend). If you can't trust your staff to perform a certain job in a certain time, I'm sure next time you can hire new people that you can trust, making integrity your number one priority when recruiting.
3) Talk to them, you need to have communication with them, it doesn't have to be a f2f chat every week/month, if you have a chat tool, google chat, or skype, ask them to be present, some of these tools can tell if the other person is not at their desk, so make sure you don't punish them for not being at the computer 24/7 (or 8 hours a day), but establish that if they are on working hours, you're expecting them to answer any of your questions regarding the project within reasonable time (since people do go to the bathroom/drop their kids off school/etc).
4) Auditing works wonders for remote work. If the project is on time, on budget, and on scope, everything should be OK, if not, make sure they know it, and to add extra effort to bring the project up to speed. Auditing a project can be as simple as making sure project deliverables are present (which should be your job), are submitted on time, scope is met, clients are happy. If they are not, than you should take corrective actions in letting know your staff they need to put more effort on X & Y, because of X & Y reason that resulted from your audit.
Hope this helped!