Elon Musk hasn't tweeted for an entire week, leaving many to wonder where the usually prolific social media user has gone. While that might be normal for most people, it's largely uncharacteristic for the billionaire who typically offers opinions on almost any topic via the micro-blogging platform. His habits as a serial tweeter have even caused legal issues in the past.

June 29th also marks Elon Musk's 51st birthday which coincided with him reaching 100 million Twitter followers. Both events are something the Tesla boss would usually celebrate online, yet he's nowhere to be seen. His last tweet was eight days ago and his last trip was on Friday, according to the ElonJet Twitter account, which tracks the billionaire's private jet flight paths. This trip was for an interview with CleanTechnica reporter Johnna Crider at the Tesla Gigafactory in Austin, Texas.