Unfortunately none of my friends seem to be very interested in trekking through Sweden. However, you can't just pick a random person and say: "Let's go!", can you? I mean it's the only contact person for a week or so.
Is there a website or something where people may get in touch?
Try starting a discussion on the couchsurfing page of the given Swedish region saying that you would like to do this or that type of trekking, for given period and difficulty, preferably include what gear would be needed; this way locals and nearby travelers may contact and join you, but beware: there is no warranty that the potential trekking partners would match your experience or expectations.
Also, check out the local scout troops: if they have the rover/adult age category, you would most probably find people interested in trekking.
There are websites you can use to find others with a similar interest in expeditions - for example, have you tried http://www.explorersconnect.com/ ? It is specifically for people looking for advice and companions for longer trips and expeditions.
