In very formal writing or speech, you can use this phrase to invite people to celebrate something or feel something together with you. Here are some common examples:
Please join me in congratulating Penny and Esteban on the birth of their first child.
Please join me in welcoming Marcus to the team.
Please join me in wishing Estelle and her family good luck on their move to Australia.
"Please join me in ___ing" is often used in formal business communications.