You mention AncestryDNA and 23&Me which are autosomal DNA tests - Leslie's answer is correct for those, see Help:GEDMatch.
But you also mention mtDNA, which is different from autosomal DNA. AncestryDNA does not test that, and 23&Me only tests enough to provide an mtDNA haplogroup, nothing to transfer. For more on mtDNA tests, see mtDNA Tests and Haplogroups. There's basically only one test that's complete enough to provide an mtDNA raw data file (called a FASTA file), and that's the FTDNA Full Sequence mtDNA test. That's the only one that can be used for direct mtDNA matching comparisons.
Currently, GEDmatch only does autosomal comparisons and matching, not mtDNA or yDNA. In the future, mitoYDNA will do mtDNA and yDNA comparisons.