Perhaps, the best known segula for fining ones intended match, shidduch, is davening at Amukah, the burial place of Reb Yonason ben Uziel, the tanna and author of Targum Yonasan ben Uziel. Various reasons for davening at Amuka being a segula to find a shidduch have been offered, but from what I've been told, none of them have actual sources - they are assumptions. The best explanation I heard was that, although we might not know the exact reason, it is a Minhag Yisroel and Minhag Yisroel is Torah.
Being that 26 Sivan is the yahrzeit of Reb Yonasan ben Uziel it is a good opportunity to mention some segulas to find a shidduch. The best thing, of course, is tefila - pouring out ones heart to Hashem for their needs – in this case for a shidduch. It's never too early to start. Those with infants, or maybe even from when the child is in the womb, should daven to Hashem, asking that there child should get a good match when the time comes. Don't wait till things get desperate and then turn to Hashem. People make a mistake, thinking they could do things on their own and only when things get tough they turn to Hashem. No matter how good a catch you or your child may be, start davening for a proper match as early as possible.
Having said that, here are some segulas for finding shidduchim, all with sources from great tzadikim:
The first four segulas are from Sefer HaMidos.
1) Say Shiras Hayam (Az Yashir) with kavanah.
2) Kiddush Levana – the hint to this is לבנה is the first letters of ב׳תולה נ׳שאת ל׳יום ה׳רביעי a maiden gets married on the fourth day. (Note: Kiddush Levana is only said by men)
3) Regularly reading the Korbanos of the Neseim (in Parshas Naso)
4) Through tefila, it is possible to change the match that was announced in Heaven.
5) A segula to find a proper shidduch is to say at the end of Shemonah Esrei, before יהיו לרצון, these two pesukim from Mishleiמָצָא אִשָּׁה מָצָא טוֹב וַיָּפֶק רָצוֹן מֵד׳ (יח,כב) and בַּיִת וָהוֹן נַחֲלַת אָבוֹת וּמֵד׳ אִשָּׁה מַשְׂכָּלֶת(יט,יד) and after that a tefila to find a good shidduch. (Dor Yeshorim, heard from Reb Avrohom Yehoshua Heschel of Radzin in the name of Reb Gershon Chanoch Henoch of Radzin)
6) Whoever says Tehilim 121 at the end of all the tefilos, before stepping back, will find a good shidduch. Also, ask for mercy for Zivug Elyon, and you will be answered first. (The last statement, according to my understanding is that one should pray for a match for lofty reasons as opposed to materialistic reasons.) (Igra D'Pirka in the name of Asara Mamaros) The source for saying Tehilim 121 is a Medrash that says Yaakov Avinu said this, praying to find his match. The first posuk says "From where will my helper (meaning wife) come?" And the next posuk says "My help will come from Hashem".
7) One who is looking for a shidduch should say the following chapters of Tehilim: 32, 38, 70, 71, 124 (Segulas Yisroel)
8) I have heard that certain tzadikim would instruct people to give 26 dollars (or $2.60 or 26 cents if they don't have the means, 26 is the gematria of yud-kei-vav-kei) to Hachnosas Kallah as a segula. This is also done by women before lighting Shabbos candles every week (could be done in the smaller denominations). (I don't have an exact source, though it seems self explanatory.)
These are just a few segulas - there are many more. If anyone knows of others please mention it in the comments, if possible with the sources.