Where Hashtags used first time?

The first use of a hashtag in social media can be traced back to one man. Chris Messina is a former Google employee who worked in developer relations and as a designer on Google+.

how do you feel about using # (pound) for groups. As in #barcamp [msg]?
— Chris Messina 🏴‍☠️ (@chrismessina) August 23, 2007

He’s been officially credited as the first person who tweeted using a hashtag. This famous tweet happened back in 2007, so it took awhile for the practice to catch on.