You can say:
1. 参加聚会 (参加to attend/to join。聚会 gatherings)
2. 从事社交活动/参加社交活动(从事to engage in/to do。参加 to attend/to join。社交活动 events/ activities/socializing)
3. Hanging out with friends:和朋友聚一聚
4. Partying: you can just say 和朋友"party", or 和朋友去party。
5. If you attend a few social events and parties in a row,you can say 和朋友跑趴(it's very colloquial)