The difference between past and present perfect , that while both are actions of the past , the present perfect is sort of a "near" past , like an action that JUST terminated or is somehow extended in the present . So since your friend must have come back from prague and the journey terminated maybe a week ,a month or more ago, then it is correct to use the past tense "found". As for you having used the verb found .. while writing ur sentence " i used "found"... you have already terminated the action , you used it ! ,,, got it ? ;)