Unless the person asking is wealthy and wants to give you the money for your business with no fear of losing it, the best thing that you can tell your family and friends who want to invest in your company is that you appreciate their support but are reserving investment opportunities to institutional investors.
Taking money from friends and family can cause issues for your business whether your business fails, is wildly spectacular, or is stuck in between.
If you take money from friends and family, there is a looming threat that you will lose your friends' and family's money. Institutional investors have a portfolio of companies, and so expect most to fail and just a few to succeed. Institutional investors want you to take big risks so that there's a higher likelihood that you'll be a big success, even if it also increases the likelihood that you'll lose their investment completely. Friends and family, on the other hand, may be overly invested in your company's success such that the loss of their investment would cause hard times and hard feelings. Even the fear that you might lose their money might prevent you from taking the risks necessary to make the company a success.