Before you communicate
It is likely that the company you are working with has their own sets of tools they use for communication and have likely supplied you with them. Ensure you are following your company's policies when it comes to those tools and how your company likes to communicate.
How to communicate
Aside from your company's rules, check out these best practices when communicating with employers.
Be polite and professional. Companies and employers are likely to reciprocate the manner in which you communicate with them. Respect them and they will respect you.
Be clear about your objective. Why you are contacting this person? What is a clear action they can take in response to your message? In general, most people are willing and happy to help, if they are clear on how they can do so.
Remember that employers are busy and have full time jobs on top of supporting students with Virtual Internships. Allow an adequate amount of time between your first message to an employer and any follow up messages you may wish to send.