Robert, who has a passion for trekking, mentioned to a friend about treking to Granada, Cordoba, Cadiz and Jerez for about 10 days.
He flew alone to Seville on 5 November 2012 but didn't board his return flight two weeks later.
His family have not heard from him since.
There have been four possible sightings of Robert following media appeals. The latest reported sighting was on 28 January 2013 in Sabinilla where a man matching Robert's description and a carrying a backpack, was seen walking at a pace towards Gibralter.
For more information you can view Sussex Police's profile for Robert here. (opens in new window)
Do you have any information?:
From the UK you can call our central freephone information line on
0800 098 8485. Calls are free from landlines but may be charged from mobiles.
From overseas you can call +44800 098 8485 but this will incur costs. Please check before you call.
Alternatively you may prefer to email any information to firstname.lastname@example.org
All information wil be treated in the strictest confidence.
You can also call Sussex Police on +44 1273 470 101.