The only one's I can think of are the two Thomson Gold Hotels. Note that although Thomson do not accept under 16 year olds at Gold hotels, other operators might, so it's unlikely to be completey child free like, say, Sandals in the Caribbean.

The hotels are the Los Gigantes in (you guessed it) Los Gigantes and the El Tope in Puerto de la Cruz.

We had a look round the the Los Gigantes a couple of years ago and it looked pretty nice and is in a very good location.

The El Tope is no longer part of the Thomson Gold program. It is still featured in the Thomson brouchure and can also be found in the Portland brouchure, but they do allow kids now.

The hotel Paradise Park in Los Cristianos is adult only. You can book direct on http://www.hotelparadisepark.com

I thought the Paradise Park had some adult only areas, but does accept children ?
I've certainly been offered it when scanning for family hotels.

hi we where at the torviscas playa hotel in fanabe last november and there was only a few children in the hotel
it depends of what time of year you go