Mr Colegate said he was "broken" and "shattered" by her disappearance which came while she was travelling in the couple’s camper van while he stayed at a farm in Gascony.
Writing on Facebook, he said: "She has was last seen six days ago when she sent me this photo. Search and rescue teams have so far found no trace of her.
“The only purpose of this post is to ask for prayers, thoughts, candles and whatever you have. I've not been saying anything, but this wonderful person believes in the power of positive thought and right now I'll take anything if it means that she can be found. I need her back. I can't face the alternative.”
Mr Colegate said he was “heading back up" the mountain to help French authorities search for his partner.
He said she had been away for a month and their last conversation had been about "how excited we were to see each other as this was her last trip before driving back".
He said searches had yielded "no sign at all" of the experienced hiker and temperatures were dropping with light snow in the area.
The couple lived in Durham before deciding to pack up their lives and go travelling after Mr Colegate nearly died from an infection.