Twitter Inc. announced a plan to raise $1.3 billion by offering convertible senior notes. This is the company’s first debt offering since going public back in November. Twitter shares fell 1.5% in late market trading. There will be two offerings each worth $650 million, the notes are expected to mature in 2019 and 2021. The microblogging site is also offering initial purchasers an option to purchase up to $100 million in each offering.