I have a valid Schengen visa in my Vietnamese passport. Can I use a Schengen Visa (Tourism) to visit Mexico ?
As stated by Timatic, the database used by airlines, yes you can.
Visa required, except for passengers with a valid visa issued by Canada, Japan, USA, United Kingdom or a Schengen Member State for a maximum stay of 180 days
Note that the official immigration website is outdated, only stating that Schengen permanent residents, and not visa holders, are visa-exempt.