Well, you know, language sometimes can be seen as a puzzle game. But in this puzzle many configurations are possible. For a literal translation, the first one seems correct. But for a more natural usage, the second one sounds better. The only thing thing is that many times the use of the pronoun is not necessary because the verb form already includes it. So maybe I would say without the "yo": “Me encontré con unos amigos que [--yo--] no había visto desde hace mucho tiempo” En cuanto a lo que han contestado, creo que tu segunda versión es la más normal. Pero... puedes decirlo así: "Me encontré a unos amigos (just simply) que // .... a quienes ... // a los cuales // ... no veía desde...." AAaaaanndddddd.... in Spain, for some reason, people tend to use the verb form "Me he encontrado", instead of "Me encontré", which is more common in American Spanish. Reasons? who knows xD the soanish would say that they use "he ido a caminar a la montaña" because the action ocurred in the same they. But a colombian mught just say "fui a caminar a la montaña"... yeah, I know, weird stuff, but when you listen carefully you will notice this that I am saying haha