Whether you were a teammate or a team lead who has been promoted to a supervisor or manager (aka: the boss), you will have to face your coworker buddies who now report to you. To put it bluntly, yes this is awkward! Plan to address the awkwardness head on and set the tone for the manager you intend to be: a transparent communicator who is focused on teamwide accountability, including self-accountability. Meet with each person one-on-one so you can let them know how you intend to operate as a manager.
This doesn’t mean you have to change your persona. You can still be join in on the idle chatter. You can still be humorous. You can even still be friends. How? Listen, even prior to being a supervisor or manager, in the workplace you should already have been drawing lines in the sand about what is appropriate and what is not appropriate to be discussing or how you are acting. This is most likely a reason why you got the promotion!
Is it difficult remaining friends? It could be, yes. You can only control your actions and behavior, not theirs. If you are acting and behaving professionally and they accept this, your friendship may remain intact with the clear boundaries drawn. However you must realize that you are no longer their peer and some workplace related conversations (as well as conversations outside of work) may need to be conducted differently. With that said, they may choose to disengage with you as a friend, unfortunately, especially if they wanted to be promoted too. If you are true to your word with how you will manage the team, they may come around.
Regardless, do not let their actions (good or bad) interfere with your interactions with the team as a whole. Implementing transparent communication and accountability with every team member will show that you are consistent and show no favoritism. The rest of the team will be watching your every move to see if you are harder or easier on your ‘buddy’. You have heard this a million times, and it is true: “actions speaker louder than words”. Act as a leader not as a boss.