Prior to the COVID 19 outbreak in the US I had a summer engineering internship at a company in Portland, Oregon. As the situation has rapidly progressed over these past few weeks the company has reached out to the interns to notify us that our start dates for this summer have been indefinitely postponed and we will be welcomed to our internships when it is safe to do so (unspecified date). I want to reach out to the company periodically to show that I am still eager for the position and am still looking forward towards the position but I am unsure of how to do so in a tactful way. What would be the appropriate method to do so without it being out of place?
Ask for an update when things start to die down.
It is going to be abundantly clear when things start to get back to normal. Governors are going to rescind shelter in place orders, people you know will be getting instructions on when to go back to work, more and more people will be outside, the death toll will drop, etc. That is the time to ask for an update as otherwise you are just sending emails to people who can't do anything about the situation and have a lot of other things to deal with.
If you really want to contact them right now, you could ask for some reading recommendations to prepare for the internship when COVID-19 comes to an end. They likely use some CAD software or programming language or have to comply with certain regulations. That would let you do something useful to prepare for your internship.