pump-and-dump
n (Stock Exchange) the practice of buying shares, generating favourable publicity about them, especially on the internet, then selling them when the price accordingly rises
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014