Remote workers can be managed effectively using tools such as Skype Instant Messaging and Skype Video Calls. It's important to meet frequently and keep those channels open and take an active role in providing updates.
Similarly, you need to create a culture where the workers do the same and contact you to give you proactive updates. If the work done is something of a specialty, like programming, then having the workers working at a remote location can give them more freedom and autonomy to make effective decisions on their own.
Just like with in office workers, it's important that deadlines are clear and that there are clear communication channels for situations where a deadline might be missed, such as if unexpected problems result.
Remote workers should be treated with the same level of professionalism as in-office workers. By keeping them in the loop, encouraging proactive communication both ways, and by utilizing the latest remote workforce technologies, remote teams can be just as effective as in-office teams.
For part-time workers, the same guidelines can help them stay motivated. With part-time workers, it's easy to forget to keep them informed, especially if they're not around for certain meetings or communications.
Here is an article with some tips for how to Keep Part-Time Employees Motivated and feeling like they're part of the group and have great skills to contribute.