"It will be a chance to network, talk, share stories. Hopefully there'll be some live tweeting but that can have its downside - everyone will be looking at their phone rather than each other."
Mr Hagger, who is an administration manager at Waiariki Institute of Technology, has been tweeting for more than four years and has racked up almost 20,000 tweets across his profiles.
"I've got lots of contacts from around New Zealand. It's a constantly changing social medium, the landscape keeps changing. There's always new people coming and going depending on the topic of the time - anything from TV through to sport. There's a couple of people I talk to all about speedway."
@Everydaymanager was his first profile but when that grew so large he set up @HagmanNZ to keep in touch with people to talk to. He also runs a blog called RandomKiwiTweeters where he blogs about his latest "follow", or Twitter profile he has followed.
Anyone who tweets and is in Rotorua on Friday can attend.
Mr Hagger is on the hunt for a suitable table decoration to enable people to recognise where the TweetUp is happening.