Hi Tim and welcome to the HUBB!
I started with a Google search on Tenerife vehicle rental, and found a site called ecanarias.com. Here is a link to the Vehicle Rentals
page. From there, you choose Motobikes North or South, which seems to have more choices of bikes, including scooters at 22 Euros per day.
You'll probably have to phone them or e-mail to make a reservation, there doesn't seem to be an online booking facility working.
"It matters not what goal you seek
Its secret here reposes:
You've got to dig from week to week
To get Results or Roses."
'One world, two wheels'
[This message has been edited by Susan (edited 28 June 2003).]