This was a concern that was discussed quite a bit in pop-science, tabloid, and conspiracy circles back when the LHC was first starting up. In short, these black holes would not destroy the Earth. Due to their small size they grow much slower than they would decay due to Hawking radiation. Even if Hawking radiation works differently than we think at those scales and they don't decay, they grow so slowly it would take eons for them to eat the Earth.

Cosmic rays with way more energy than the LHC bombard the Earth all the time. So the fact that the Earth still exists would tell us that these micro black holes, if they form, won't destroy a planet in less than billions of years.