Unfortunately, I doubt that there are very many texts like that in the Church Fathers, simply because people (children) were engaged and married very shortly after (or even sometimes before) puberty hit, so that pre-marital sex was an extremely rare problem. Thus, most of the literature take the viginity vs. marriage standpoint because that's simply how society was run: you either were celibate or were married, there wasn't really the type of time period we have today where peoplewere running around going on dates for 10 and 15 years before they got married. So, I guess if you're looking for something from a Saint saying "You should save yourself for marriage," I wouldn't really know who to reference. Fwiw, though, here are some documents on virginity that might give you some ideas...
St. Ephraim the Syrian - On Virginity
St. Gregory of Nyssa - On Virginity
St. Ambrose of Milan - Three Books Concerning Virgins
Also, there is an essay titled Sex And the Spirit of our Age
by Fr. John Weldon Hardenbrook, which is in an appendix (pp. 136-141) of the book Preserve Them, O Lord: A Guide for Orthodox Couples In Developing Marital Unity
by Fr. John Mack, and it might be of some help.