Transfermarkt is ok, but it is important to see when the player joined the club he is listed as being contracted to on there. Chances are (although not always the case) they have moved on if they moved to the club over two seasons ago.
To check who they play for now, you could always try and type their name and club into google and see if there are any recent news articles that confirm where he plays, such as a match report etc.
I know that some countries have good news sites or football specific sites that can help. Such as Zambia (http://zambianfootball.co.zm/ http://www.zambianfootball.news/ http://www.fazfootball.com/) and some countries have good facebook pages that can be helpful such as Rwanda (https://www.facebook.com/groups/247482408639668/ https://www.facebook.com/rwafootball/?__tn__=%2Cdk%2CP-R&eid=ARCAC0nPMfAyea5Us5lJcWkWe8Xujge6WptBHJwbXc_utU6iLKzZ0EbqCkvjcCysbbQNPk7IGvnM8WIK)