Generally speaking, the current SLOWLY is designed for meeting new friends around the world.
User's real identity is kind of hidden - using avatars instead of profile pic, nickname instead of real name - in order to let people speaking freely, having genuine communication without bias and concerns. So, unfortunately, you are not able to search specific users based on any ID.
However, after receiving more feedbacks from users, we understand that it would be a beautiful way to use SLOWLY to communicate with your real life friends as well.
So, we have already added this feature to our development wish list. Hopefully, we could put it into practice in the future. Please stay tuned.