Madonna wears one and her love of Kabbalah is well documented. If you visit The Western Wall in Jerusalem you will most likely be approached to buy one. Rooted in Jewish mysticism some believe you tie one around your left wrist to ward off evil spirits. Another tradition says a single women should wear it until it falls off. She will then meet the man she is going to marry.
If marriage is your goal I think rather than wearing a red string on your wrist, try donning a red string bikini. That will speed the process.