Runstrom had spells in Italy with Chievo and Fiorentina before returning to Sweden to join Hammarby.
"I believe that Bjorn will be another great prospect for the future for Fulham," Coleman told the club's official website.
"We are committed to not only challenging for a top 10 spot this term but also to building for the future and I think that Bjorn will be another one to watch.
"He has exceptional levels of stamina and gives the opposition defence little time for rest or composure, because of his hard work and commitment."