I wouldn't trust the pick up lines from Runnersworld, they would probably freak out the poor girl, and make her run for her life. I have some good ones that people here might like to try on there runs. I would just approach and be friendly first. Ask does she come here often, and show her scenic forest trails that you can run through together, she might be interested. If the weather is cold and raining take your top off and offer to give it to her. Tell her that her pace is very good. If she isn't carrying any gels or energy bars, offer her some thing. If she has none you can compliment her. Say "I see your not carrying any thing to refuel, is that because you think your fat, because your not". Now that you have made her feel comfortable and at ease, you can do the pick up lines.
1. You are like the Bekele of this park(where ever you are running with her)
2. Running with you is better then being able to keep up with Bekele. I want to be beside you for ever.
3. This park has some nice lakes, trees and hills, but the most amazing part of it is you.
4. Bekele has run with some great runners, Sihine, Tadese, Geb to win gold medals, but he hasn't won with the best runner of all, you. To me you are gold.