Is One Week Friends manga still on going? Finished the anime and very curious on whats gonna happen next. Is the manga complete or is it still on going?
No, it is still ongoing according to Wikipedia. At top right of the page under "Original run", it says "January 21, 2012 – ongoing". 

Sometimes, Wikipedia doesn't update the information or the status is left like that when the series is on a long unexplained hiatus. Just to be sure, in the Volumes section of that page, it says that the release date for Volume 7 is April 22, 2015, which shows that the next volumes is in the works.

Also, Manga-Updates says the same thing under "Status in Country of Origin" (6 Volumes (Ongoing))

According to a post on Anime News Network provided by Torisuda, Volume 7 is the last one.


  The sixth compiled volume of Matcha Hazuki's Isshūkan Friends. (One Week Friends) manga is announcing on Tuesday (26/07/2014) that the seventh and final volume of the manga will be released in Japan on April 22, 2015.