If I understood your question properly, then my five-cents are:
A method is orderly logical arrangement of (a way of doing) actions to accomplish some task (e.g., a series of actions made to generate a triangulated finite element model based on CAD model data).
A technique involves using technical means in a purposeful way to achieve a goal (e.g., producing a multi-material rapid prototype by a multi-head 3D printing).
A tool is a hardware, a software, or a hybrid instrument (or implement) that is needed and used to carry out a function and eventually to accomplish some task).
I think this interpretation can be applied in the context of co-creation
A method is more general overall 'approach' to your co-creation process, the general 'way' of doing it: for example you can choose to do a series of activities with end-users in their own natural context-of-use (a 'situated' method), you can focus on people's opinions, you can focus strongly on using prototypes, or focus on more abstract 'future scenario's', and so on.
A technique is a more specific 'procedure': how to concretely carry out some activity, and it forms part of a method. For example there are various techniques for 'eliciting user needs' or 'envisionment of new concepts', or 'evaluation techniques' etc.
A tool can be whatever concrete 'thing' you need (next to the people involved and the context) to do what you want to do. For example you may need wall, tape, a photocamera and printer as part of a 'user needs elicitation technique' in which you want people to photograph what they find interesting, put it on the wall and have them cluster these pictures together.
Often the word 'tool' is associated with specifically designed 'co-creation tools' such as multi-touch tables or boxes with tinkering materials or a set of diaries you can send to people for a 'context mapping technique' and so on. Here things can get blurry as these 'tools' are often designed with a specific 'technique' in mind: they are the physical embodiment of the technique. But an ordinary whiteboard can be a very important tool that says nothing about the technique for which you need it.
When the method is weak (very new, vague, etc) the difference between method and technique can be blurry as well. Politically scientists/engineers will try to 'coin' their own ways of working 'as a method' or 'technique' and then hope it catches on and 'really becomes something'. In that sense one could say that a method only really becomes a method if many other people start using it as such. (This is of course very different in the exact sciences where optimal 'methods' for solving this or that equation can be very strictly defined and proven to exist even if nobody cares about using them for anything).
Finally: in *practice*, at least in co-creation practices, I find the existence of the tool often precedes formal definition of the technique, and techniques often precede formal description of the method. So although it seems as if you first (should) have a method, within which you pick a certain number of techniques, for which you then go to the shop to buy or make the necessary tools, in reality it often goes the other way around: one starts by already selecting/creating and using tools, and after adapting and changing the tools to ones practical needs one realizes that one is 'actually' doing something that could be described as applying something of a technique, and when a number of related techniques can be put together and some consistent reasonable story can be told about them in which they all hang together, something of a 'method' seems to emerge.
There is also a rhetoric aspect of your question. If you want to highlight that it is a scientific way of inquiry you call it a method (Lat. methodus, Gr. methodos), if you want to highlight the craftmanship of it you call it a technique (Gr. techne), and if you want to highlight the practicality or materiality of it you call it a tool.
Dr Arvola, I resonate with you. This is what my above interpretations carry concerning an enabler of addressing a challenge. Regards, I.H.
