Investors are flocking to Lyft and Airbnb.The stock market has delivered solid returns for investors so far this year, and excitement about the new bull market is palpable. If you're looking for compelling businesses to buy and hold for the long haul, you should focus on how those companies look as long-term investments and if they align with your overall portfolio objectives.Your risk appetite should also define the types of stocks you buy. If you have the risk tolerance to put cash into growth stocks righ ...