If you miss someone who is currently far away, you might dream of writing letters in a long distance relationship. If you have the address, you can start to write a letter. If you have their social media or email, start to write them a communication. Be cool.
The problem will be when you don’t have any leads as to where to direct your communication. If you don’t know their email addy or social media handles, you can still write and post it in your own account. A mutual friend might read it and help you to make the connection by forwarding your writing.