Standard & Poor’s Ratings has assigned Twitter a junk-grade rating while also describing it as having strong growth prospects. The ratings agency gave the company a BB- corporate credit rating, which places it firmly in the middle of junk-grade territory. The outlook is described as stable. Shares of Twitter fell 5.7% to $40.12 in late afternoon trading on Thursday. The stock has lost more than a third of its value in the year to date. S&P predicted Twitter would see healthy growth in active users and revenue.