Growing my rental portfolio

[Brooks Everline]

Looking to expand upon my rental portfolio.  I currently have one rental that I have owned since 06.  I have a very small mortgage with lots of equity build up.  It is in a sought after neighborhood, school district, etc..and produces serious cash flow ($700-800)/month.  Looking for opinions as to whether or not to sell this income property to use the large chunk of cash to move into multi family or hold onto it and find other creative means of financing multi family deal?  BiggerPockets thoughts greatly appreciated.